Thanks, Thunderhead! Excellent explanation! For those of us who work on our own rigs, with only the internet as teacher, videos like this are gold. 1984 4WD Toyota pickup 22R
Dude. This video is perfect. I have little to no idea when it comes to old-school style setups. And this was super easy to understand, and now know which aftermarket dizzy I need!
One of the best explanations I've seen. I have a 1979 Viking Deckboat with a Chevy small block 305 in it. I bought it not running thinking I could fix it. Well so far it's been a hole in the dirt (can't get it in the water) I'm throwing money into. Initially the guy I bought it from said it just needed a fuel pump. So I replaced the pump and then found the Starter was bad. So replaced it. Then I found the Spark Plug wires were not right. So fixed that. Then as I was playing with those I found the Rotor in the Distributor would turn in my hand. I looked at it and it seated on the shaft good and actually looked fairly new. So I pulled the Distributor and grabbed the bottom gear and the Rotor still turned in my hand. Now I'm kinda stumped. This Distributor doesn't have a Vacuum Advance on it and I can't find an old style, similar Distributor. Some have said just replace it with a modern electronic ignition but all the Distributors I can find still have the Vacuum Advance on them. I don't have the experience to switch it. I think the coil should be changed also but I really don't know what to do about this ignition system. Stumped in South Carolina!
Thank you - I bought a running 1951 Ford Flathead on an engine stand. It ran great on the stand. I got it home and built my own test stand - no problem. The engine runs great. The only thing is that the engine did not come with a vacuum advance unit on the distributor. I ordered one from O'Reilly Auto Parts and it should be in this afternoon. I've never installed a vacuum advance unit, but I'll give it a try. Thanks.
There is a component that you may have passed over. It is the speed of the engine and the time it takes the fuel air mixture to burn. When at low RPM you don't want the mixture to start burning too early or you will have the explosion taking place too early in the compression stroke of the cylinder, making the piston fight this explosion to complete it's upward movement, if you don't advance the timing at a high RPM the explosion will happen too late and it will finish the burn too far after top dead center and the power will be robbed by filling a cylinder with a piston that is descending. The air fuel mixture doesn't take long to burn, but that small amount of time has to fit into the mechanical timing of the piston and valves to make the most of the energy.
Been following you around YT for a little while and have enjoyed your content, but it's really amazing to me how many times I come to the internet to answer a question and end up finding something from your catalogue that answers it. Appreciate you doing these. The vacuum advance doesn't seem to be working on my 75 F100 but I'm getting ready to sell it. Sounds like I can pass this baton over to the new owner (I'll be glad to disclose it but not something I'm going to worry much about).
Diggin your videos. I bought an 85 cj7. Not gonna lie I’m in over my head. I’ve had a misfire since I bought it. I thought it went away but it’s back. I did plugs wires cap rotor and retired it and it seemed great. Now it got a little cold and she’s back. It could be surging. To me it feels like it’s not getting gas and it’s a hard misfire. Really stumped on it. I’m gonna change the pcv valve I am leaking oil and burning oil and it does run rough. I enjoy learning all these things and taking a step back in time. Appreciate your knowledge and time!
Hey Ryan, what type of carb does it have? The biggest tuning aid is to get a wideband o2 as you know what your fuel curve is doing. Fuel and timing needs to be a harmonious balance. Search “Thunderhead289 wideband” I have a full parts list with links in that video
Hey Ryan, what type of carb does it have? The biggest tuning aid is to get a wideband o2 as you know what your fuel curve is doing. Fuel and timing needs to be a harmonious balance. Search “Thunderhead289 wideband” I have a full parts list with links in that video
Dude!! I love how ur explanations r straight & to the point its very clear u completely understand thus u kno how it works!! I understand wen u speak & no studdeding u dont have alot of "um,um" my only question is where u been & how come iv never seen or heard of u well no more i have subscribed fantastic work pal keep em comn!
Thank you. I have a 1952 Buick...it's my first classic, and I am trying to troubleshoot issues with it. I'm sure a replacement vacuum advance cannister exists, but I am glad to know that it's not everything.
Ported vacuum advance is for smoggers. It came in in the early-mid 70's. Proper vacuum advance will help keep your engine running cooler and will aid at cruise, which is low load, lean mixtures.
If your engine is timed at lets say 10 before tdc . With the vacume advance disconnected . If you were to rev the engine it will accelerate to lets say 3000 rpm in a certain amount of time . Then , hook up the vacume advance canister . There will be on change at idle because you connected it to a timed port . But ... When you rev the engine again to 3000 rpm , it will rev to that point faster and with less effort . When you rev your engine even with very little throttle the vacume will drop . This drop causes the power valve to temporarily open and causes a rich mixture . This condition can and will benefit from more ignition timing from the quick response of the vacume advance . A rich mixture burns slower . A lean mixture burns quicker . A rich mixture burns cooler and a lean mixture burns hotter . I noticed the first comment that said that timed port is a smog or emissions thing , but it's not . I've worked on many 50s 60s and all through out the 80s . There was a trend starting in the mid 70s or so to slow or electronically control the advance in the ignition . They ran the engines lean as possible and controlled the ignition timing AND introduced 02 into the exhaust . Retarded ignition timing along with oxygen injected into the exhaust burned more hydrocarbons and fluorocarbons CFCs and pcbs in the exhaust . And we had much less power but better girl economy but engines did not last as long because of the heat created by lean and late . Ported vacume gives a much more responsive part throttle and much better part throttle driveability With timed port you tap the throttle and the engine vacume recovers much more quickly . When hooked to manifold vac , you have to set the timing with the dist hooked up and with each increment of throttle you loose ignition timing until the mechanical advance runs up to its limit . FORD , did much with ignition timing and vacume advance was something they knew about . On many manual trans Ford's of the 60s had a dual vacume canister on the dist . One went to timed port and the other to manifold vac . It was to return the vacume advance to zero FAST when you let off the gas so you could shift or downshift faster . What happens if you advance the distributor while it idling? The engine runs faster and faster until it starts misfiring . The engine becomes more efficient until it's mechanical limits are reached .
@@jamessignorelli852 Lean mixtures burn slower and need more lead. Ported vacuum advance is for smoggers. Rich mixture burns faster, which is why vacuum advance falls off at WOT and high load.
Good explanation I knew nothing about vacuum advance and I can't give a class today either, but it did help me. I can't say that I would be able to tell the difference with or without, but it's always good to know though.
I had a K-Code 1965 Mustang - bought new. Dual point distributor, no vacuum advance. 14-16 mpg @ 65 mph was about the best it would do. Of course, I didn’t buy the car/engine for fuel efficiency. It was a very strong pulling car. ❤️ed it!
@@jonathanmorrisey5771 That’s what I said in my original post. Setting the dwell was fun (not). The accepted method was place a cigarette paper between one set of points, and measure the dwell, with a dwell meter, on the other set. Then switch the cigarette paper to the other set of points. Cigarette paper was advised because it’s so thin the points will not be measurably held off the cam and thus distort the readings.
I have one question regarding the older engines (1987 Ford Escort). So when you are adjusting timing with the timing light, there is usually mark on the timing belt cover and one on the harmonic balancer. Do you unplug the vacuum advance hose, plug it and then adjust the distributor for the two marks to line up?
So I've got a question. The vehicle is a 7600 lb 1981 c30. These heavy trucks run with no cats, no o2 sensors, just a fully mechanical Quadrajet like a 60s or early 70s vehicle. It's at 8*-10* initial timing I forget which. Someone installed an HEI with and adjustable can which I've never messed with. I have the truck maintained, dialed, and tuned almost perfecto but it's off a hair at "launch". I like to drive it hard and fast when tuning. Say I'm at a light and punch it. There's a slight delay and then it charges foward HARD. Its way faster than it should be. 😁 I'm trying to get rid of that first little delay. The carb is on point I'm sure of it. Can I correct that hesitation by going to manifold vacuum rather than ported how it is now? Would playing with the adjustable vacuum pod finesse my tune? All I need to do is gain torque under load coming from a stop. Pretend I'm loaded with a heavy trailer. Please and thank you.
Great video. What about the advance canister itself. There is an adjustment inside of it. As you know , slide in a small Allen wrench and turning will change things. Could you pass along your thoughts about this? Also (you might laugh at this this) but do you have a troubleshoot engine consulting service? I’d pay you right now for over the phone help. I’m not kiddening.
Manifold vacuum is the only source for vacuum advance if you want it to function as intended. Ported vacuum advances the spark too much when accelerating because there is vacuum even when the gas pedal is on the floor which is not correct.
65sohc Once the plates open, manifold vacuum decreases while venturi vacuum starts to increase from zero. At 1/2 throttle, manifold vacuum is much lower than venturi vacuum. Most people don't understand this principle.
The orifice from which the ported vacuum receives its signal is a fraction of an inch above the closed throttle blade, basically at the level of the transition slot. As soon as the throttle is cracked open that orifice is exposed to full manifold vacuum. The venturis are much higher and affect fuel flow through the boosters by increasing air velocity.
Just subscribed to your great channel. I have a crate 383 stroker in my 77 Monte Carlo that came with mechanical advance. Also installed 700R4 tranny & 3.73 rear gears. 480/470 at the flywheel. The cam is Lift: .500 / .510, Duration @ .050: 225 / 231, Centerline: 108, Fair idle, Street mild performance usage, The vacuum advance cannister is connected to distributer but crimped (not hooked up to any vacuum). As it is, my timing settings are maxed out for maximum engine output. Car runs perfect! If I hook up vacuum advance, can I simply leave those timing settings alone?
Thunderhead289 Prior to explaining this concept, it would be best to explain the differences between "vacuum" such as ported, venturi and manifold vacuum. Many many shadetree mechanics and a few experts do not know the differences and often choose the wrong vacuum hose or port on the carb thinking they have it right.
Yes thanks. The problem folks don't understand is the functions of ported vacuum. It's no vacuum at idle and venturi vacuum above idle or a vacuum that has zero relationship with engine load. With that understanding, folks should figure out that when mashing the gas pedal fully, they are working the mechanical advance and the vacuum advance together which places too much total vacuum at higher RPM and not enough advance when at idle. Ported vacuum is NOT the method for vacuum advance needs unless the manufacturer has designed their application to work only with ported which is a totally different animal in design for outcome.
You are misreading my opinion about vacuum advance. I am all for it but only with manifold vacuum as a source. I owned several late '60's and early 70's GM cars and trucks and understand this point rather well. Shade tree mechanics and racers don't. Like the above "ported" source idea, there's no timing advance at idle which defeats the purpose of the entire principle. Vacuum advance features requires vacuum at idle on up to cruise LOADS. No one has said were give a crap about emissions here, only performance and cooler operating temperatures aka a good running machine. Yes, ported venturi vacuum was misstated above however, venturi vacuum does exactly that and won't work. Even ported vacuum isn't the correct method to utilize the benefits that were designed into vac adv.
So at WOT is there any difference in ignition timing whether the engine is running directl manifold vacuum advance, ported vacuum advance, or no vacuum advance? Hint: I know the answer.
Hey brother, been having a great time looking through your videos as a new content creator. I don't want this to come across the wrong way, but I feel you maybe a little off the mark with your understanding of vacuum advance and it's operation. I'm not sure how I can make contact with you, but I will try and make a video in the coming week of my experience with it as a former carburettor and ignition specialist and the different methods in which it operates. Again, I hope this didn't come across the wrong way. Look forward to hopefully working together with you somehow in the future. Rob.
Hey rob, You are probably one one the smart ones - I tried to “simplify” this for folks to a degree because every time I start talking about cylinder pressures as it relates to burn time/ flame propagation, cylinder volume charge density and so on it just goes right over folks head. Technically when you are cruising you have a much less dense charge - that cylinder charge will have a slower burn time. When you stand on it, cylinder pressures rise and likewise the burn time is much quicker - same concept between a compression test with throttle closed vs open. More pressure = less timing (among other factors), and less pressure = more timing (again, among other factors) Anyway, I’m a really wordy guy so sometimes I have just tried to present things in a way that will have folks use something properly and not get too invasive - perhaps this was a disservice on this video. You can contact me at brotherford289@gmail.com if you want to talk - I always enjoy knowledgeable folks.
I just want to know. If I lightly press on the accelerator and the vehicle feels like its losing power, is my vacuum pump damaged. Ignition timing is right. Fuel air mixture is right. The vacuum hoses are not damaged. When i accelerate harder the engine regains its power. The vehicle is an '87 Nissan 1400. All stock parts with a Hitachi carburettor.
Great as usual thunderhead! At some point I'd like to hear what you consider a mild street cam vs a mild street/race cam vs a all out race cam.your about the only 1 listen to as most leave things out from what I was taught. I use to put TV cans in my street motors but lately I've used comp cans hi energy. What do you prefer?
I'm running a voodoo cam with. 515 lift roughly.. It's a weekend car should I run the vacuum advance?? I've checked timing with it hooked up and seen 60° of timing... Thx in advance
What would you do with a vacuum advance port that is hooked up to a computer box? Mine is driver side fender behind battery. Has a channel for the breather tube, too. Electric connections hook into existing harness. Not sure where they end up. I no longer have a Spark Control Computer on breather. No emissions stuff. Just this box.
I have an HEI Distributor on my 6 cylinder Corvair that has an Isky 280 cam in it. I'm getting exhaust popping on deceleration and I thought I had exhaust leaks. Someone told me to remove the vacuum from the distributor and guess what, no more popping. This is the same distributor I used on another engine with the same cam and there was no popping. Why am I getting exhaust popping now? Someone else says to use a distributor vacuum delay valve. Can you explain how this valve works?
How much advance typically does the vacuum advance add to the timing if it is set at 12 degrees without. I have a pole school accel dual point distributor on my SBF. I don’t remember how far the timing advanced when the vacuum advance was added. That was many years ago. Right now I have the timing set at 21 degrees. I cant hear pinging when accelerating because the exhaust is to loud.
Quick question on your thoughts: 1977 ford f100. 302 engine. Starts great. Idles great. Revs and drives great. But when coming to a stop at a stop sign or light, the engine dies..... Starts back up with pedal pressed to floor. If I kick it into neutral when coming to a stop the engine will stay running.....
So for all in I take my base timing plus the max advance of my dizzy which is 15 degrees right? I want around 34 degrees all in so my base needs to be around 19?? I had it set to 13 but she lagged alot and my plugs were quite black... Now at 19 she rips and no pinging that I can hear... Plug straps look ok so far... Major learning curve at the moment
I have an 79 F350 with a 460 that someone put an Edelbrock 1405 on ..right now it runs ok when "cold" but when I drive it for 20 min or so then when I try to let it idle it acts like it wants to die. Put a vacuum gauge and it hovers in 15mg which is "late timing". At "cold" it pulls 21mg or so, seemed healthy...I had been adjusting the idle mixture screws because even when I first bought the truck it seemed to run rough at idle - shaking every so often. I figured that was just partly from having such a big engine. I spend some time messing with the idle screws to get max vacuum (got about 21mg or so) and lowered the idle rpm to around 700. Of course putting it in gear on automatic tranny that RPM drops even more so now becuase it is less happy when warmed up, when in gear is when it acts like it wants to die, so at stop signs, etc. So I don't trust it to take it through town too much. So now even after my attempted adjustments it runs worse than when I got it when fully warmed up. I tried to check base timing but some idiot painted a giant white stripe on the line so I cant read it . the engine label says stock is 8 degrees. I have to get down in there and clean up the line markers and repaint them Yesterday I decided to test the vacuum advance (which in this case they connected to ported vacuum). Well it turns out it just sucks air, and doesn't move - I can hear the air just go right through it. So, I need to replace that - so that seems to probably be why I have a really bad idle. And it sounds like I need to connect the advance to manifold vacuum, and then maybe I will get proper idle at full warmup. It seemed to run better when I first bought the truck (still ran rough at idle though, you could feel the shaking every so often) but I think that is because they just raised the idle RPM to overcome the crap idle. They had the idle around 1000ish I'm hoping putting on a new vacuum advance unit and connecting it to manifold will solve my crappy idle issues. It seems to run fine other than that right now, no problems accelerating or taking off from a stop sign even. Just bad loping and wanting to die after its fully warmed up. Throws me off a bit that it seems to run better when cold even with the advance not working.
Could be two things - generally if something runs better cold than it does warm with the choke fully open is because the mixture is too rich. a colder engine needs more fuel since the intake is cold so fuel does not atomize as well. once the engine warms, less fuel is needed for a running ratio since the fuel is atomizing much more efficiently. on the other hand, if you have excessive underhood heat, the fuel will start vaporizing in the lines, and even if it doesnt vaporize, it gets very warm and less dense which alters the AFR. id imagine with a 460, you dont have a lot of room under the hood. search "thunderhead289 return line" i really battled this in virginia till i added a return line to my galaxie. also, always have a clean air filter, a dirty unit is restrictive and works as a choke to a degree and will create some of the same symptoms
I hacked away at it for a while today, got the new vacuum advance installed, checked the timing seemed OK, checked for vacuum leaks, didn't seem to find any. Finally I pulled the idle jet rods out of the carb and blew air through the holes..and now - seems to run much much better. I saw a video on UA-cam where they show how to do that and thought it was worth a shot. Maybe I just had some dirt in there, don't know. It seems to be running OK for now, or at least, when I took it to the gas station, it was running pretty good and didn't want to die at stop signs. Thanks for the responses! Your videos are excellent
Thanks ThunderHead - another very helpful video, much appreciated. I am running a Blueprint 347 with the pertronix billet vacuum advance distributor. I am running ~12-14 degrees initial and 32-34 degrees total mechanical with my vacuum advance connected to manifold vacuum. I get about 16 inches of vacuum at idle. Everything is great, except I am getting spark knock when cruising on the highway when I tip in to very light throttle. Am I just running too much mechanical timing? Should I run vacuum advance off of ported? Do I need an adjustable vacuum advance canister to lessen the advance this is giving me during this tip in scenario? I'm stuck. Thanks for your help and your experience!
Hello thanks for this video I have a 1950 Chevy Coupe with a 216 engine that I replace the points and condenser inside the distributor and replaced it with pertronix igniter. The car starts fine and drives but I feel like the car is not running as smooth and as loose as it used to before when it had the points and condenser. I posted a video of the car running on Facebook and some people commented that it could be the vacuum advance. What is your opinion? The car runs like if it is being held back, And like you mentioned on the video I really have to give it gas to run down the road
Why would you use the term " pull in ignition timing 2:16 " but when the vacuum is pulling the diaphragm it is advancing timing increasing the numbers, the term pulling would seem losing timing numbers not increasing numbers as you have stated.....
Definitely Carb Tuning how to. I've been trying to tune the carb on my 302 and I get it running good one day then the next it runs like garbage. I've been doing this for more than 2 weeks now and overall it never gets any better. I've set the idle timing to 11° btdc and am using a vacuum gauge to try and set the carb.
From what I can tell its an Edlebrock Performer 600 cfm carburetor. I know the carb is good as it was rebuilt with the engine so that shouldn't be the issue.
+Dalton Elliott I have a pretty strong distaste for the Edelbrock carb after many years of experience with different carb types. Never trust when something says they rebuilt something. There are only a select few that can "rebuild" anything automotive correctly.
Yeah I know it not a great carb but I got it for free from a friend so I'm not too upset. Any advice on tuning it in? I've let the engine get up to temp, tried tuning it for the highest idle vacuum and it never really gets above 15" of vacuum.
Thanks for the insight. I don’t think my mechanical advance is working as I rev the engine. The marks on my distributor only move 3-6 degrees approx. on revving. Is this correct?
I'd bet your mechanical advance is pretty hung up or the springs are wore out. You can pop the cap and should be able to rotate the rotor via the advance mechanism. If it barely moves or fails to return after moved, you can be sure that you have a mechanical advance issue
So my vacuum doesn’t work. Nor it was connected. But car seems to run just fine.. I bought it like that. Should I fix or leave it alone? Like I said. Runs fine
Great video. It left me with a question though. If i buy an vacuum advanced distributor, and wanted to go with a racier cam profile, could I just disconnect the vacuum part and plug it and still use the distributor, or does that distributor need the vac to function properly. Like if I bought an vacuum operated 123 distributor which is without points and controlled by a microprocessor and revcounter to set the timing, then i should be able to unplug the vacuum if I wanted a more tracked spec engine, like a new cam and such? I'm actually buying a 123 distributor for my classic mini as "we speak", but want to buy the correct version.
I have a sbc and I have a eselbrock carburetor with vacuum advanced hooked up to it. But I do have a stock cam and a eselbrock manifold with a 650 cfm 4 barrel. Should I just use manifold port instead of ported.? I'm going to also set my distributor at 8 degrees time advance.
Question, I have a 72 hurst olds just rebuilt it has a comp cams 42-241-4 cam 490 lift 280 duration 110 lobe. Timing currently set at about 20 Deg ATDC when punched engine is pinging pulling timing back to around 15 no ping but engine won't idle unless set at 800-900 rpm in gear. Please help. Thank you.
Thunderhead289 I have a 73 olds Delta 88. I have a demon 625 carb. Changed intake manifold. Hei distributor with vacuum advance. I have the 73 chassis manual for the car also. I'm having issues. The book says 12° at 1100rpm. It's not right or I'm not doing something right. I'm getting soot thru tailpipe so I'm thinking timing is off. It's running rich you can smell the fuel. I did the Venturi box idle set screw like you illustratrate in other video. Long story shorter where would you start with troubleshooting. I've been at it for over a month now off and on. Thanks in advance
Would you consider a Melling MTC-6 on a 454 still in the range for vacuum advance working? It's got 112 LSA and .449 lift (I think) duration is like 208/209? Been awhile since I looked at the specs, it's a stage 2 towing cam in an 81 C30 with a Turbo 400 behind it. Thanks in advance!
The 63 nova I just bought has a t where the vacuum for the vac advance is being shared with what I assume is a pcv valve and they both go to manifold. Any potential issues here? I’m chasing down a loss of power on acceleration and after rebuilding carb, changing mechanical fuel pump, changing points contacts, and a new vacuum advance the last thing I can think is it that or a timing issue.
I have a 351 in a 93 bronco. It has a vacuum leak. When parked, I can romp on it with no issues. It just idles a little high. However, on the highway it tries to die if I give it a lot of gas. Could this be caused by something in the vacuum advance?
Hi There, Would you put a distributor with vacuum advance on it on a 1985 Chevy C60 with a 366 big block and a Holley 4160? This is a big, slow truck made for hauling rather than speed. I'm wondering if a vacuum advance would help my fuel economy.
I have a chevy 305 and noticed it doesn't have a vacuum advance, so do i have the mechanical one then ,and should i get a distributor that has one ,answer from anyone appreciated,,thanks
Where does the vacuum advance hose hook2 on the 302 Ford 84 model on the carburetor and is it both to have suction all the time or just when you give it gas
hey man. ove your channel. I was hoping you. might have some insigt into some performance issues im having. i hsve an 82 GMC vandura. And just recently it started bogging down and losing power but usually just when it shifts into 3rd. I drove it with a vacuum guage attached to manifod vac and wn it bogs down the vacuum goes to around 5 and below. . could this bog be a vacuum issue? i have a vacuum advance on order as im pretty sure mine doesnt work. BUt i also think that it wasnt working for a long time. Also. I had an old timer mechanic convince me recently to bypass all my emissions stuff, and he unplugged all the hoses from my two TVS switches. Do those now need to be removed and plugged off? in other words...could they create a vaccuum leak if left in without any lines attached? im scratching my head for a wekk over this bog
My dad has a 66 F100 that I helped him swap a 390 from a 65 galaxy into. Has a mild cam, headers, Holley 600 and for some reason when the vacuum advance is plugged into manifold vacuum the truck dies. There are no vacuum leaks in the hose and the gaskets are all new. It will also idle only with part choke. Carbs been rebuilt twice. Any help is much appreciated.
You invited questions so mine is: Do you have any knowledge to share concerning performance oriented centrifugal advance spring kits (for example Mr. Gasket 925D)? I'm running a mild 289 (F303 cam, Edelbrock Performer RPM heads, 650CFM Holley w/vacuum secondaries, headers, stock distributor w/Pertronix. Car is about 2400 pounds, 5 speed, 3.54 rear end. Thanks in advance.
Everyone makes ignition timing difficult, but it’s actually very easy. Outside of your throttle settings, you want the spark to fire as soon as possible without timing creep at idle (too light of springs will sporadically pull idle timing) So after you set your idle initial timing, choose springs that pull in timing as soon as possible without causing spark knock (pinging). Set initial by setting your transfer slots tova square, and adjusting your initial timing along with your mix screws to set your idle - you have about 1 full turn of the idle screw from square t slot to play with before you get an overexposure scenario. I personally run on ported vacuum. Typically I see that for most folks with vacuum canisters that pull more than ten degrees that this works best. Thunderhead289
ThunderHead289 Thanks for the quick reply. And thanks for reminding me about possible idle creep. The good news is that light springs can possibly tailor the timing to an optimum curve; the bad news is the greater propensity for failure. And thanks for the Holley tip.
As odd as this sounds, I have found that I snap the heavy springs more! Transfer slot theory works for all transfer slot carbs - with running a vacuum gauge and a wideband gauge side by side, I have seen the best results all that I have mentioned above. Also, I super simplified this video - when you open your throttle, cylinder pressure also rises - the higher the pressure, the denser the mixture, and the quicker the fuel charge will burn. So cruising needs more timing, into the throttle takes less. Remember, the goal is to fire the mixture as soon as possible on the power stroke to use as much of that stroke as possible.
He has excellent videos on setting up Holley four barrels. OEM carbs are not tunable. If a problem has been reliably isolated to the carb it is either repair or, more likely, replace.
Because as you open the throttle plates, there is less restriction to the air flowing into the engine. That is why manifold vacuum is highest at idle, and lowest at wide open throttle. Randy
Hey man I got one for ya! Okay, I just bought a 1984 f150 Custom short box 2wd with a 5.0 in it. And ive been doing a budget build on it and I just got my mad 6al box and my blaster 2 coil wires up and working, but now when I try and run my tach wire to the back of my factory tach from the tach output onthe msd box I get nothing. Now fyi this truck did not come stock with a tach, I robbed the cluster and wiring harness out of another junk truck and just wired it up to mine and it was working until the msd swap, now nothing. Help me out if you will!
hi! Great video and thanks for the clear explanation. Am I understanding that correctly that a vacuum advance valve has absolutely nothing to do with a rough idles speed? I have tested the valve and the pin doesn't move at all while sucking the hose..I only can open it with a screw driver. I have a rough idle/bit revving too on my 1983 Honda Accord and can not find the source of the issue...thanks!
The diaphragm is probably damaged/deteriorated and has a vacuum leak. What will happen is if your engine is set at stock base timing is running retarded because it relies on the vacuum advance to run at its sweet spot. A quick fix is advancing the base timing to overcompensate for the lack of vacuum advance. Only problem is as explained here when you are at wide open throttle your timing would be more advanced than desire and you'll probably get loss of maximum potential power or pinging if it's advanced too far.
Seems to be that vacuum canister has a leak... those engines usually initial ignition timing is 6 bdtc with the vacuum advance disconnected.. if you have rough idle start by checking and tuning the basics, such as spark plugs gap, check condition of the spark plugs cables, the rotor and the cap also the right gap for the points in the distributor... assuming the carburetor has no internal leaks and it's in good conditions and valves are well calibrated
The guy who built my motor a 350 chev w/ RV cam. I told him I wanted low end torque sometimes it acted like it wanted to ping on acceleration. so sometime after I check where the timing was at idle and it was at 25 and also notice he had manifold vac not ported hoocked up so I change it to 10° initial timing vac disconnect and them hooked up to ported vac. What I noticed now is the centrifugal weights where sticking so fix that and now if I rev it quickly the idle does not come backs all the way down to about 750. I think he put in some really light springs so the weights start flying out just above idle. So I'm going to check it. and I got me a curb kit for the advance. Any thoughts on this will be appreciated. Yes I want good low end but also good mid range. Someone on u tube said he likes having total advance by 2400. What do you think?
What vehicle is this engine in? So-called "RV" cams are typically low duration, low overlap designs that build a lot of low end torque and flatten out above 4500 rpm. Cylinder pressure off idle is high so they don't need a fast timing curve with a lot of advance down low. Full advance by 2400 may be ok for a light performance car with short gears and a performance cam but is too early for a torque motor in a heavier vehicle as it would make it prone to preignition. Total mechanical advance of around 36 degrees is good but I would think having it all in by around 3000 would be safer.
@@65sohc total timing is 69° 15 ° above normal i know. Harmonic balancer is in good cond. I think its the 8° of advance valve timing that he set that causes the ing timing to have to be 15° advanced. Ro run right. No pinging either.
@@mtnman6278 Have you actually checked the timing yourself? 69 degrees seems impossible. If I'm not mistaken advancing the cam creates even more low rpm cylinder pressure and wouldn't call for more ignition advance. But if it runs good what the heck.
If you figure vacuum advance is about 15 degrees+centrifugal 25, that's 40. In order to have 69 total initial would have to be 29. I'm surprised the engine would even start with that much initial timing. Something isn't right. If those are actually the numbers you are seeing on your timing light I would suspect the marks on the balancer are off.
So I know this was two years ago but my girlfriend has an 82 GMC sierra s15 and we can not figure out where to attach the vacuum hose to the carb... any suggestions on which carb port it is?
Most carbs have a full time vacuum port and another that supplies vacuum over about 1000-1200 rpm or thereabouts. I've always found I got better results using the full time port (usually lower down on the carb). This was with both small and big block Chevy engines with headers and mild aftermarket cams in fairly light cars. I got much crisper throttle response and the side benefit of slightly better gas mileage. Your engine/vehicle combination my prefer the ported vacuum (usually higher up on the carb). Why not try each for a day or two of normal driving and see which you find better? Just be sure to block of any unused ports. Let me know your results if you would.
I bought a 70 Impala with a lot of stuff wrong with it. Got most of the major things fixed, but I'm having a hard time knowing where to put my vacuum hose from valves to the 2 bbl carb. Bought a Haynes manual and that was pretty useless and I can't find any stock photos of a 69 or 70 with the air cleaner off. I just want it to run right. Not fast
Borrow or buy (Harbor Freight has decent cheap ones) a vacuum gauge, connect it to a port, test if it has vacuum (needle is up at idle) and when you rev the engine the needle should drop (no vacuum). If you connect it to a port that does that you should be good.
@@danwells7691 If you have no vacuum at idle and then vacuum starts as soon as you open the throttle a bit that is ported vacuum.If you then punch the throttle vacuum should instantly go to 0.
Question: Just completed tune-up on 318 Mopar Engine 2 barrel Holley; idles and revs great until I hookup vacuum advance; starts missing when reving RPMs; What's the problem? Remove vacuum advance and runs great again!?
Can too much timing cause me to stumble than take off when I mash the peddle ? Throttle response is really good with regular driving. But if I go from idle to (wot) it falls on its face than takes off like crazy ? Would you call timing or bigger square nozzle ? I have a summit carb. Running manifold vacuum on stock cam. 12 degrees initial timing.
Timing that works is a reflection of your idle mixture. - they both work hand in hand. It sounds more like your transfer slots may be over exposed at idle which are in charge of some of the off idle transition. Also, make sure you don’t have play in your accelerator pump. That can easily cause a bog off the line
I have a small block chevy and car runs when vacuume advance is unhooked but car dies and back fires when I hook it up can u tell me what would cause that....
Hey dude, sooo... I have a wrangler with a 383 stroker 220cc heads, big mutha thumpr cam and a Holley hp street 750 carb. The thing is that it takes like 6-8 trys for the engine to run, it turns and then it feels like it chokes and dies. The mechanic told me that it was because the engine is cold but I have seen engines like mine on UA-cam that turn on right away. Also, it feels rough under load. Do you think the distributor has something to do with it ? The total timing is at 38 I was told, 15 initial timing and I can’t remember the other one.
Your Heads are too many CC's and a mutha thumper is a botique cam designed primarily for a lopey idle, and not performance. Next time call Chet Herbert cams and tell them your parts/goals and they will grind you a cam that makes much more power. You can use heads that big or bigger in a drag race setup, but for the street/woods you would be better with smaller heads. Even down the 180 cc runners This increases velocity and low end torque. What you want in a Wrangler.
Don Rutter the main purpose of the Jeep is sand drags not rock crawling. I put that cam because I had it from I project that I was going to do but I never finished it and I sold it. And the heads are 220cc CNC ported.. sorry for the typo.
I have a really dumb question.... my vacuum advance hose is missing from my distributor. If i re-attach it, does it plug into my carburetor?? I just got my 73 Charger back on the road after 4 years of slumber. She's running hot, and my idle is funky. I have an 850 CFM Holley double pump carburetor. Where do i plug it in? Im a female gear head, and I work on the car myself, but this is a new one for me... Im kind of embarrassed to ask...
It would help to know some more details about your engine. That is a lot of carburetor for anything built in 73. That engine would originally have used ported vacuum which does not affect idle quality. Therefore it would be important to know why the idle is "funky" and, just as importantly, what you consider funky. Thunder 289's Galaxie has a rough idle, owing to the camshaft overlap, but it sounds anything but funky. To answer your question, your 850 has a vacuum port on the side of the primary metering block that is used for vacuum advance. Base timing needs to be set first.
Bottom of carb is manifold vacuum, right side of carb front bowl is ported vacuum. Use manifold vacuum. You arent worried about emissions (ported) you want it to run good, and not hot (ported). The Duntov cammed 64' corvette was the first to use ported vacuum, GM engineers admitted it was a mistake, engineers say all motors with ported distributor vaccum were an attempt to meet emissions, and the motors run hotter. Ported vacuum is another abomination you can thank the state of California for.
If I am understanding correctly, I plug the vac hose when I am setting my initial and the advance timing. If I have an aggressive cam (280 degree intake/286 degree exhaust), I use manifold vac, or ported vac?
Manifold. And any cam around 300 degrees or over you definitely dont use any vacuum advance. Bigger cams, you set the timing somewhere in the 16-24 degree range at idle, and build a stop on your centrifigul advance to full advance at 36. Big cams need a lot of initial timing. Bigger cams need the most. They dont make enough vacuum to run a vacuum advance properly. The low vacuum causes "dithering" that means the vacuum cant open the centrifigul advance all the way, so it never ends up at the same spot at idle, causing erratic idle RPM's and stalling. Older cast iron heads have poor volumetric efficiency so need the most timing advance compared to modern computer designed aluminum heads. The more duration you have (valves open longer) the bigger the pistons you need. Valves open longer steal compression.
i agree with you - but only in excessive scenarios. a rich mixture that is too rich cannot be properly ignited, a lean mixture will get extremely hot from the compression and want to preignite. if either of these scenarios (below 10:1 or above 14.5:1) exist, the carb needs to be adjusted immediately or permanent damage can and will occur.
I have a 69 Skylark Buick L77 350 4B 10:25:1 compression.. 285hp 400 ft lbs.. It pings. I have it at 4 degrees static. I run super 91. Under low RPM and a good load, it will ping. I can get it to stop by going 2 degrees static.. But I lose so much power. When the motor is cold and warming up, no ping. Once it is warmed up.. Some pinging.. Any suggestions?
what carb, intake, and cam style are you running? also, what is your elevation and relative driving temps? and when you say static, do you mean initial timing BTDC? are you using a timing light to determine your settings?
Quadrajet . Engine is factory original. and yes.. BTDC. I am at 6000 feet. 9000 feet for HP reason as we run at times single digit humidity here in Colorado. Yes.. I use timing lights. Temps here as of late are 70 F. Normally I run 1.5 degrees advanced for every 1000 feet. But on this Buick, i can not do it. Must be because of its high compression as it was made to burn Ethyl pump gas back in the 60's. I am considering a 4 row aluminum radiator and a 165 thermostat.
well, i cant chalk it up to too lean of mixture as you are lacking oxygen at those levels to the point that you may have to even pull jet out of it. im curious what your plugs look like - you seem very competent in these affairs. the lower you can keep the engine temp (dont operate below 160) the cooler the cumbustion chambers, and the better they will resist preignition. let me know on the plugs.
The only way to know for sure is to connect a timing light. Check timing with vacuum advance disconnected, then with it connected at full vacuum. To get full vacuum at idle and thus max out your vacuum cannister you will likely need to use either a vacuum pump, such as Mighty Vac, or suck on the hose like Thunderhead289 did.
what would you recomend for totel timing on a 1979 351w 2150 motor craft 2bbl c4 trans chines short tube fox body headers duel 2.5 exhaust h pipe glass packs no smog junk on 87 octane?
I have a question my car feels like its ristricted like to only go 45 miles an hour its a 235 engine i have a stainles metal line from the carb to the advance. .so my friends say the line is to thick its a 1/4 line they say the line restricks the distributor from turnning more so the car can go faster is that true .. I hope I make sence please any one let me know
Gregory Frost - I just follow the directions on the box. If you turn it counter clickwise to start then with the allen wrench turn it in until it just stops. Then hook the lvacuum line back up. with the engine warm take it up on the freeway or a deserted road and at cruising speed start to accelerate and try to detect any pinging. If not, then keep backing the vacuum advance out 1 turn and rehook up the vacuum line then take it for a spin listening for any pinging. So you keep doing this until the motor pings. When it does then go back and turn the vacuum can in a turn. Then hook up your vacuum line and you should be set.
This is an old video where I taught along conventional lines - I have since said heck all that and teach how I do things because honestly conventional carb teaching sucks and doesn’t perform as well
I have a 1972 chevy C-10 pick-up, it's been rebuilt with a RV cam in it. but what's it's doing noiw is, when I coming to a stop sign or a stop light it dies on and someone says it might be my vacuum advance or air leak in one of my vacuum lines.
Set timing to 36 degrees total, restrict vac advance to only 10-15 degrees and plug into manifold vacuum. Check for vacuum leaks in the hoses and the carb base. What carb do you have?
One engineering point. People think the fuel/air charge explodes to drive the piston down. That is incorrect. The fuel/air charge burns across the cylinder from the spark plug to the far end of the chamber over a few milliseconds to build needed pressure. What is not mentioned is that max cylinder pressure is needed at 10° ATDC for maximum leverage. Mechanical and vacuum advance are used to build the needed pressure at all speeds and loads.
Question .. my Cleveland 351 bored 30 mild cam stock crank , 650 edlebrock my little prob is when iam at cruising with very pressure on the pedal I get a pop through the exhaust it happens in 3 rd and 4 gear . Just thought I would pick your brain .. thanks
seems like too much cruising ignition timing off hand. several things can play into this including air fuel ratio. if you have vacuum advance, remove it and see if the issue persists - this will help diagnose the problem. get back with me here.
Well I remove the vacuum advance hose , plugged off both ports one on carb other distributer and problem gone , can the advance be changed or adjusted because the vacuum advance can be tuned with a Allen key
ah , good deal. so it was bringing in too much advance. the adjustable units are a bit tricky. if you lesson their advance, you will also lower the vacuum at which they will drop out of the timing equation. so for example, you have one pulling in 15 degrees of timing that drops out at 13 inches of vacuum. adjusting it will make it add in only say 10 degrees, but now it drops out at 10 inches of vacuum. my issue is that they are still adding in extra timing now at a higher load then they were before. its just gray area. this is the point where you have to listen for pinging or stumbling issues.
Well in the gray area , there is no ping or stumbling . Now is it possible to adjust the timing so I can run with the advance hooked up to improve fuel economy and easier starting ( just that when the advance was hooked up the choked worked , one press on the pedal and it fired up and run on high idle then when warm it kicked down)
thanks for all the videos, you have helped many times. I have a 302 out of an explorer with a light cam, i was having issues trying to get on it high rpm, i installed fitech, same problem, so i added pcv, got better then all the sudden an afterfire and now its rough low rpm.. someone said i might need to add vaccum?? maybe vaccum canister?
Thanks, Thunderhead! Excellent explanation! For those of us who work on our own rigs, with only the internet as teacher, videos like this are gold. 1984 4WD Toyota pickup 22R
Dude. This video is perfect.
I have little to no idea when it comes to old-school style setups. And this was super easy to understand, and now know which aftermarket dizzy I need!
One of the best explanations I've seen. I have a 1979 Viking Deckboat with a Chevy small block 305 in it. I bought it not running thinking I could fix it. Well so far it's been a hole in the dirt (can't get it in the water) I'm throwing money into. Initially the guy I bought it from said it just needed a fuel pump. So I replaced the pump and then found the Starter was bad. So replaced it. Then I found the Spark Plug wires were not right. So fixed that. Then as I was playing with those I found the Rotor in the Distributor would turn in my hand. I looked at it and it seated on the shaft good and actually looked fairly new. So I pulled the Distributor and grabbed the bottom gear and the Rotor still turned in my hand. Now I'm kinda stumped. This Distributor doesn't have a Vacuum Advance on it and I can't find an old style, similar Distributor. Some have said just replace it with a modern electronic ignition but all the Distributors I can find still have the Vacuum Advance on them. I don't have the experience to switch it. I think the coil should be changed also but I really don't know what to do about this ignition system. Stumped in South Carolina!
Thank you - I bought a running 1951 Ford Flathead on an engine stand. It ran great on the stand. I got it home and built my own test stand - no problem. The engine runs great. The only thing is that the engine did not come with a vacuum advance unit on the distributor. I ordered one from O'Reilly Auto Parts and it should be in this afternoon. I've never installed a vacuum advance unit, but I'll give it a try. Thanks.
There is a component that you may have passed over. It is the speed of the engine and
the time it takes the fuel air mixture to burn. When at low RPM you don't want
the mixture to start burning too early or you will have the explosion taking
place too early in the compression stroke of the cylinder, making the piston
fight this explosion to complete it's upward movement, if you don't advance the
timing at a high RPM the explosion will happen too late and it will finish the
burn too far after top dead center and the power will be robbed by filling a cylinder
with a piston that is descending. The air fuel mixture doesn't take long to
burn, but that small amount of time has to fit into the mechanical timing of
the piston and valves to make the most of the energy.
Been following you around YT for a little while and have enjoyed your content, but it's really amazing to me how many times I come to the internet to answer a question and end up finding something from your catalogue that answers it. Appreciate you doing these. The vacuum advance doesn't seem to be working on my 75 F100 but I'm getting ready to sell it. Sounds like I can pass this baton over to the new owner (I'll be glad to disclose it but not something I'm going to worry much about).
Diggin your videos. I bought an 85 cj7. Not gonna lie I’m in over my head. I’ve had a misfire since I bought it. I thought it went away but it’s back. I did plugs wires cap rotor and retired it and it seemed great. Now it got a little cold and she’s back. It could be surging. To me it feels like it’s not getting gas and it’s a hard misfire. Really stumped on it. I’m gonna change the pcv valve I am leaking oil and burning oil and it does run rough. I enjoy learning all these things and taking a step back in time. Appreciate your knowledge and time!
Hey Ryan, what type of carb does it have?
The biggest tuning aid is to get a wideband o2 as you know what your fuel curve is doing.
Fuel and timing needs to be a harmonious balance.
Search “Thunderhead289 wideband”
I have a full parts list with links in that video
Hey Ryan, what type of carb does it have?
The biggest tuning aid is to get a wideband o2 as you know what your fuel curve is doing.
Fuel and timing needs to be a harmonious balance.
Search “Thunderhead289 wideband”
I have a full parts list with links in that video
Smoking??
Wow, VERY well explained. I agree with below, "no wasted verbage". Thanks sir! Subscribed.
Dude!! I love how ur explanations r straight & to the point its very clear u completely understand thus u kno how it works!! I understand wen u speak & no studdeding u dont have alot of "um,um" my only question is where u been & how come iv never seen or heard of u well no more i have subscribed fantastic work pal keep em comn!
Thank you. I have a 1952 Buick...it's my first classic, and I am trying to troubleshoot issues with it. I'm sure a replacement vacuum advance cannister exists, but I am glad to know that it's not everything.
Ported vacuum advance is for smoggers. It came in in the early-mid 70's. Proper vacuum advance will help keep your engine running cooler and will aid at cruise, which is low load, lean mixtures.
If your engine is timed at lets say 10 before tdc .
With the vacume advance disconnected .
If you were to rev the engine it will accelerate to lets say 3000 rpm in a certain amount of time .
Then , hook up the vacume advance canister .
There will be on change at idle because you connected it to a timed port .
But ... When you rev the engine again to 3000 rpm , it will rev to that point faster and with less effort .
When you rev your engine even with very little throttle the vacume will drop .
This drop causes the power valve to temporarily open and causes a rich mixture .
This condition can and will benefit from more ignition timing from the quick response of the vacume advance .
A rich mixture burns slower .
A lean mixture burns quicker .
A rich mixture burns cooler and a lean mixture burns hotter .
I noticed the first comment that said that timed port is a smog or emissions thing , but it's not .
I've worked on many 50s 60s and all through out the 80s .
There was a trend starting in the mid 70s or so to slow or electronically control the advance in the ignition .
They ran the engines lean as possible and controlled the ignition timing AND introduced 02 into the exhaust .
Retarded ignition timing along with oxygen injected into the exhaust burned more hydrocarbons and fluorocarbons CFCs and pcbs in the exhaust .
And we had much less power but better girl economy but engines did not last as long because of the heat created by lean and late .
Ported vacume gives a much more responsive part throttle and much better part throttle driveability
With timed port you tap the throttle and the engine vacume recovers much more quickly .
When hooked to manifold vac , you have to set the timing with the dist hooked up and with each increment of throttle you loose ignition timing until the mechanical advance runs up to its limit .
FORD , did much with ignition timing and vacume advance was something they knew about .
On many manual trans Ford's of the 60s had a dual vacume canister on the dist .
One went to timed port and the other to manifold vac .
It was to return the vacume advance to zero FAST when you let off the gas so you could shift or downshift faster .
What happens if you advance the distributor while it idling?
The engine runs faster and faster until it starts misfiring .
The engine becomes more efficient until it's mechanical limits are reached .
@@jamessignorelli852 Lean mixtures burn slower and need more lead. Ported vacuum advance is for smoggers. Rich mixture burns faster, which is why vacuum advance falls off at WOT and high load.
Good explanation I knew nothing about vacuum advance and I can't give a class today either, but it did help me. I can't say that I would be able to tell the difference with or without, but it's always good to know though.
I had a K-Code 1965 Mustang - bought new. Dual point distributor, no vacuum advance. 14-16 mpg @ 65 mph was about the best it would do. Of course, I didn’t buy the car/engine for fuel efficiency. It was a very strong pulling car. ❤️ed it!
Really cool 💪
K-code did not run a vacuum advance.
@@jonathanmorrisey5771 That’s what I said in my original post. Setting the dwell was fun (not). The accepted method was place a cigarette paper between one set of points, and measure the dwell, with a dwell meter, on the other set. Then switch the cigarette paper to the other set of points. Cigarette paper was advised because it’s so thin the points will not be measurably held off the cam and thus distort the readings.
I have one question regarding the older engines (1987 Ford Escort). So when you are adjusting timing with the timing light, there is usually mark on the timing belt cover and one on the harmonic balancer. Do you unplug the vacuum advance hose, plug it and then adjust the distributor for the two marks to line up?
Your videos are great! Thank you for making and sharing them.
So I've got a question. The vehicle is a 7600 lb 1981 c30. These heavy trucks run with no cats, no o2 sensors, just a fully mechanical Quadrajet like a 60s or early 70s vehicle. It's at 8*-10* initial timing I forget which. Someone installed an HEI with and adjustable can which I've never messed with.
I have the truck maintained, dialed, and tuned almost perfecto but it's off a hair at "launch".
I like to drive it hard and fast when tuning. Say I'm at a light and punch it. There's a slight delay and then it charges foward HARD. Its way faster than it should be. 😁
I'm trying to get rid of that first little delay. The carb is on point I'm sure of it.
Can I correct that hesitation by going to manifold vacuum rather than ported how it is now? Would playing with the adjustable vacuum pod finesse my tune?
All I need to do is gain torque under load coming from a stop. Pretend I'm loaded with a heavy trailer.
Please and thank you.
Great video. What about the advance canister itself. There is an adjustment inside of it. As you know , slide in a small Allen wrench and turning will change things. Could you pass along your thoughts about this? Also (you might laugh at this this) but do you have a troubleshoot engine consulting service? I’d pay you right now for over the phone help. I’m not kiddening.
Manifold vacuum is the only source for vacuum advance if you want it to function as intended. Ported vacuum advances the spark too much when accelerating because there is vacuum even when the gas pedal is on the floor which is not correct.
Not true. Once the throttle is opened off idle you will get the same vacuum gauge reading whether connected to ported or direct manifold vacuum.
65sohc Once the plates open, manifold vacuum decreases while venturi vacuum starts to increase from zero. At 1/2 throttle, manifold vacuum is much lower than venturi vacuum. Most people don't understand this principle.
Disagree...When full throttle, manifold vacuum is almost zero while ported is maximum.
The orifice from which the ported vacuum receives its signal is a fraction of an inch above the closed throttle blade, basically at the level of the transition slot. As soon as the throttle is cracked open that orifice is exposed to full manifold vacuum. The venturis are much higher and affect fuel flow through the boosters by increasing air velocity.
When the blades are opened fully, what is the ported vacuum at this point?
Just subscribed to your great channel. I have a crate 383 stroker in my 77 Monte Carlo that came with mechanical advance. Also installed 700R4 tranny & 3.73 rear gears. 480/470 at the flywheel.
The cam is Lift: .500 / .510, Duration @ .050: 225 / 231, Centerline: 108, Fair idle, Street mild performance usage,
The vacuum advance cannister is connected to distributer but crimped (not hooked up to any vacuum). As it is, my timing settings are maxed out for maximum engine output. Car runs perfect! If I hook up vacuum advance, can I simply leave those timing settings alone?
Thunderhead289 Prior to explaining this concept, it would be best to explain the differences between "vacuum" such as ported, venturi and manifold vacuum. Many many shadetree mechanics and a few experts do not know the differences and often choose the wrong vacuum hose or port on the carb thinking they have it right.
I did make a video over this topic back in the day!
ua-cam.com/video/p6w9-BDu1JU/v-deo.html
Yes thanks. The problem folks don't understand is the functions of ported vacuum. It's no vacuum at idle and venturi vacuum above idle or a vacuum that has zero relationship with engine load. With that understanding, folks should figure out that when mashing the gas pedal fully, they are working the mechanical advance and the vacuum advance together which places too much total vacuum at higher RPM and not enough advance when at idle. Ported vacuum is NOT the method for vacuum advance needs unless the manufacturer has designed their application to work only with ported which is a totally different animal in design for outcome.
You are misreading my opinion about vacuum advance. I am all for it but only with manifold vacuum as a source. I owned several late '60's and early 70's GM cars and trucks and understand this point rather well. Shade tree mechanics and racers don't. Like the above "ported" source idea, there's no timing advance at idle which defeats the purpose of the entire principle. Vacuum advance features requires vacuum at idle on up to cruise LOADS. No one has said were give a crap about emissions here, only performance and cooler operating temperatures aka a good running machine. Yes, ported venturi vacuum was misstated above however, venturi vacuum does exactly that and won't work. Even ported vacuum isn't the correct method to utilize the benefits that were designed into vac adv.
So at WOT is there any difference in ignition timing whether the engine is running directl manifold vacuum advance, ported vacuum advance, or no vacuum advance? Hint: I know the answer.
No, there is no difference. However, when WOT, who cares? The focus on vac adv is gas mileage and reductions in heat.
Thank you. Nice video
Could you please tell what do you mean my mild, stock and big cam ?
I didn’t get that part .
Hey brother, been having a great time looking through your videos as a new content creator.
I don't want this to come across the wrong way, but I feel you maybe a little off the mark with your understanding of vacuum advance and it's operation. I'm not sure how I can make contact with you, but I will try and make a video in the coming week of my experience with it as a former carburettor and ignition specialist and the different methods in which it operates. Again, I hope this didn't come across the wrong way.
Look forward to hopefully working together with you somehow in the future.
Rob.
Hey rob,
You are probably one one the smart ones - I tried to “simplify” this for folks to a degree because every time I start talking about cylinder pressures as it relates to burn time/ flame propagation, cylinder volume charge density and so on it just goes right over folks head.
Technically when you are cruising you have a much less dense charge - that cylinder charge will have a slower burn time. When you stand on it, cylinder pressures rise and likewise the burn time is much quicker - same concept between a compression test with throttle closed vs open. More pressure = less timing (among other factors), and less pressure = more timing (again, among other factors)
Anyway, I’m a really wordy guy so sometimes I have just tried to present things in a way that will have folks use something properly and not get too invasive - perhaps this was a disservice on this video.
You can contact me at brotherford289@gmail.com if you want to talk - I always enjoy knowledgeable folks.
I just want to know. If I lightly press on the accelerator and the vehicle feels like its losing power, is my vacuum pump damaged. Ignition timing is right. Fuel air mixture is right. The vacuum hoses are not damaged. When i accelerate harder the engine regains its power. The vehicle is an '87 Nissan 1400. All stock parts with a Hitachi carburettor.
Great as usual thunderhead! At some point I'd like to hear what you consider a mild street cam vs a mild street/race cam vs a all out race cam.your about the only 1 listen to as most leave things out from what I was taught. I use to put TV cans in my street motors but lately I've used comp cans hi energy. What do you prefer?
Informative video what’s your recommendation 302 sbf with an RV cam looking at an MSD ready to run vacuum advance with no need for a trigger box
Can you do a video about the vacuum amplifier, i have a laye 70s dodge and have no clue how it works.
I have a question about my 66 VW bug.it has 1600 motor,and I would like to know if I can plug my vacuum unit and is it as a regular distributor.
I'm running a voodoo cam with. 515 lift roughly.. It's a weekend car should I run the vacuum advance?? I've checked timing with it hooked up and seen 60° of timing... Thx in advance
I would like to see someone answer this I have the same 60
What would you do with a vacuum advance port that is hooked up to a computer box? Mine is driver side fender behind battery. Has a channel for the breather tube, too. Electric connections hook into existing harness. Not sure where they end up.
I no longer have a Spark Control Computer on breather. No emissions stuff. Just this box.
I have an HEI Distributor on my 6 cylinder Corvair that has an Isky 280 cam in it. I'm getting exhaust popping on deceleration and I thought I had exhaust leaks. Someone told me to remove the vacuum from the distributor and guess what, no more popping.
This is the same distributor I used on another engine with the same cam and there was no popping. Why am I getting exhaust popping now?
Someone else says to use a distributor vacuum delay valve. Can you explain how this valve works?
How much advance typically does the vacuum advance add to the timing if it is set at 12 degrees without. I have a pole school accel dual point distributor on my SBF. I don’t remember how far the timing advanced when the vacuum advance was added. That was many years ago. Right now I have the timing set at 21 degrees. I cant hear pinging when accelerating because the exhaust is to loud.
Quick question on your thoughts: 1977 ford f100. 302 engine. Starts great. Idles great. Revs and drives great. But when coming to a stop at a stop sign or light, the engine dies..... Starts back up with pedal pressed to floor. If I kick it into neutral when coming to a stop the engine will stay running.....
torque converter staying locked up?
My Distributor is dirty and the vacuum advance is frozen up, I was thinking about sending it to Advanced distributors is that a good place?
So for all in I take my base timing plus the max advance of my dizzy which is 15 degrees right? I want around 34 degrees all in so my base needs to be around 19?? I had it set to 13 but she lagged alot and my plugs were quite black... Now at 19 she rips and no pinging that I can hear... Plug straps look ok so far... Major learning curve at the moment
I have an 79 F350 with a 460 that someone put an Edelbrock 1405 on ..right now it runs ok when "cold" but when I drive it for 20 min or so then when I try to let it idle it acts like it wants to die. Put a vacuum gauge and it hovers in 15mg which is "late timing". At "cold" it pulls 21mg or so, seemed healthy...I had been adjusting the idle mixture screws because even when I first bought the truck it seemed to run rough at idle - shaking every so often. I figured that was just partly from having such a big engine.
I spend some time messing with the idle screws to get max vacuum (got about 21mg or so) and lowered the idle rpm to around 700. Of course putting it in gear on automatic tranny that RPM drops even more so now becuase it is less happy when warmed up, when in gear is when it acts like it wants to die, so at stop signs, etc. So I don't trust it to take it through town too much.
So now even after my attempted adjustments it runs worse than when I got it when fully warmed up. I tried to check base timing but some idiot painted a giant white stripe on the line so I cant read it . the engine label says stock is 8 degrees. I have to get down in there and clean up the line markers and repaint them
Yesterday I decided to test the vacuum advance (which in this case they connected to ported vacuum). Well it turns out it just sucks air, and doesn't move - I can hear the air just go right through it. So, I need to replace that - so that seems to probably be why I have a really bad idle. And it sounds like I need to connect the advance to manifold vacuum, and then maybe I will get proper idle at full warmup.
It seemed to run better when I first bought the truck (still ran rough at idle though, you could feel the shaking every so often) but I think that is because they just raised the idle RPM to overcome the crap idle. They had the idle around 1000ish
I'm hoping putting on a new vacuum advance unit and connecting it to manifold will solve my crappy idle issues. It seems to run fine other than that right now, no problems accelerating or taking off from a stop sign even. Just bad loping and wanting to die after its fully warmed up. Throws me off a bit that it seems to run better when cold even with the advance not working.
Could be two things - generally if something runs better cold than it does warm with the choke fully open is because the mixture is too rich. a colder engine needs more fuel since the intake is cold so fuel does not atomize as well. once the engine warms, less fuel is needed for a running ratio since the fuel is atomizing much more efficiently.
on the other hand, if you have excessive underhood heat, the fuel will start vaporizing in the lines, and even if it doesnt vaporize, it gets very warm and less dense which alters the AFR. id imagine with a 460, you dont have a lot of room under the hood. search "thunderhead289 return line" i really battled this in virginia till i added a return line to my galaxie.
also, always have a clean air filter, a dirty unit is restrictive and works as a choke to a degree and will create some of the same symptoms
I hacked away at it for a while today, got the new vacuum advance installed, checked the timing seemed OK, checked for vacuum leaks, didn't seem to find any.
Finally I pulled the idle jet rods out of the carb and blew air through the holes..and now - seems to run much much better. I saw a video on UA-cam where they show how to do that and thought it was worth a shot. Maybe I just had some dirt in there, don't know. It seems to be running OK for now, or at least, when I took it to the gas station, it was running pretty good and didn't want to die at stop signs.
Thanks for the responses! Your videos are excellent
I was going to guess the vacuum cannister was shot.
Thanks ThunderHead - another very helpful video, much appreciated. I am running a Blueprint 347 with the pertronix billet vacuum advance distributor. I am running ~12-14 degrees initial and 32-34 degrees total mechanical with my vacuum advance connected to manifold vacuum. I get about 16 inches of vacuum at idle. Everything is great, except I am getting spark knock when cruising on the highway when I tip in to very light throttle. Am I just running too much mechanical timing? Should I run vacuum advance off of ported? Do I need an adjustable vacuum advance canister to lessen the advance this is giving me during this tip in scenario? I'm stuck.
Thanks for your help and your experience!
With a bigger cam, can you run a vacuum pump to get manifold vacuum back and use a vacuum advance?
Hello thanks for this video I have a 1950 Chevy Coupe with a 216 engine that I replace the points and condenser inside the distributor and replaced it with pertronix igniter. The car starts fine and drives but I feel like the car is not running as smooth and as loose as it used to before when it had the points and condenser. I posted a video of the car running on Facebook and some people commented that it could be the vacuum advance. What is your opinion? The car runs like if it is being held back, And like you mentioned on the video I really have to give it gas to run down the road
Why would you use the term " pull in ignition timing 2:16 " but when the vacuum is pulling the diaphragm it is advancing timing increasing the numbers,
the term pulling would seem losing timing numbers not increasing numbers as you have stated.....
Definitely Carb Tuning how to. I've been trying to tune the carb on my 302 and I get it running good one day then the next it runs like garbage. I've been doing this for more than 2 weeks now and overall it never gets any better. I've set the idle timing to 11° btdc and am using a vacuum gauge to try and set the carb.
what carb do you have? if you give me some details on it, i may be able to direct you to the source of your issues.
From what I can tell its an Edlebrock Performer 600 cfm carburetor. I know the carb is good as it was rebuilt with the engine so that shouldn't be the issue.
+Dalton Elliott I have a pretty strong distaste for the Edelbrock carb after many years of experience with different carb types. Never trust when something says they rebuilt something. There are only a select few that can "rebuild" anything automotive correctly.
Yeah I know it not a great carb but I got it for free from a friend so I'm not too upset. Any advice on tuning it in? I've let the engine get up to temp, tried tuning it for the highest idle vacuum and it never really gets above 15" of vacuum.
are you cammed?
Great video. However I always thought vacuum advance was to compensate for volumetric efficiency.
Thanks for the insight. I don’t think my mechanical advance is working as I rev the engine. The marks on my distributor only move 3-6 degrees approx. on revving. Is this correct?
I'd bet your mechanical advance is pretty hung up or the springs are wore out. You can pop the cap and should be able to rotate the rotor via the advance mechanism. If it barely moves or fails to return after moved, you can be sure that you have a mechanical advance issue
So my vacuum doesn’t work. Nor it was connected. But car seems to run just fine.. I bought it like that. Should I fix or leave it alone? Like I said. Runs fine
Great video. It left me with a question though. If i buy an vacuum advanced distributor, and wanted to go with a racier cam profile, could I just disconnect the vacuum part and plug it and still use the distributor, or does that distributor need the vac to function properly.
Like if I bought an vacuum operated 123 distributor which is without points and controlled by a microprocessor and revcounter to set the timing, then i should be able to unplug the vacuum if I wanted a more tracked spec engine, like a new cam and such? I'm actually buying a 123 distributor for my classic mini as "we speak", but want to buy the correct version.
I have a sbc and I have a eselbrock carburetor with vacuum advanced hooked up to it. But I do have a stock cam and a eselbrock manifold with a 650 cfm 4 barrel. Should I just use manifold port instead of ported.? I'm going to also set my distributor at 8 degrees time advance.
Question, I have a 72 hurst olds just rebuilt it has a comp cams 42-241-4 cam 490 lift 280 duration 110 lobe. Timing currently set at about 20 Deg ATDC when punched engine is pinging pulling timing back to around 15 no ping but engine won't idle unless set at 800-900 rpm in gear. Please help. Thank you.
Hello Thank you for the info. Which vacuum port do I connect to on my Edelbrock 1406? Passenger or driver side? Stock sbc 283
Thunderhead289 I have a 73 olds Delta 88. I have a demon 625 carb. Changed intake manifold. Hei distributor with vacuum advance. I have the 73 chassis manual for the car also. I'm having issues. The book says 12° at 1100rpm. It's not right or I'm not doing something right. I'm getting soot thru tailpipe so I'm thinking timing is off. It's running rich you can smell the fuel. I did the Venturi box idle set screw like you illustratrate in other video. Long story shorter where would you start with troubleshooting. I've been at it for over a month now off and on. Thanks in advance
Would you consider a Melling MTC-6 on a 454 still in the range for vacuum advance working? It's got 112 LSA and .449 lift (I think) duration is like 208/209?
Been awhile since I looked at the specs, it's a stage 2 towing cam in an 81 C30 with a Turbo 400 behind it. Thanks in advance!
Why would my 1984 f150 302 have small surge in an out at steady load. Thank you
The 63 nova I just bought has a t where the vacuum for the vac advance is being shared with what I assume is a pcv valve and they both go to manifold. Any potential issues here? I’m chasing down a loss of power on acceleration and after rebuilding carb, changing mechanical fuel pump, changing points contacts, and a new vacuum advance the last thing I can think is it that or a timing issue.
? Hi, I have a Series 3 Landrover, it has a non-return valve on the pipe close to the vacuum, is that required...
I have a 351 in a 93 bronco. It has a vacuum leak. When parked, I can romp on it with no issues. It just idles a little high. However, on the highway it tries to die if I give it a lot of gas. Could this be caused by something in the vacuum advance?
Hi There,
Would you put a distributor with vacuum advance on it on a 1985 Chevy C60 with a 366 big block and a Holley 4160? This is a big, slow truck made for hauling rather than speed. I'm wondering if a vacuum advance would help my fuel economy.
great video. so if two new vacum advanced distributor cause backfires in the exhaust at a certain rpm/timing it could be the vacuum ?
No, not the vacuum. Backfiring from the exhaust is from a rich AF mixture. Backfiring from the carb is a timing issue.
I have a chevy 305 and noticed it doesn't have a vacuum advance, so do i have the mechanical one then ,and should i get a distributor that has one ,answer from anyone appreciated,,thanks
Just go ahead and get a whole new dizzy. They sell new hei distributors on eBay for $50
Where does the vacuum advance hose hook2 on the 302 Ford 84 model on the carburetor and is it both to have suction all the time or just when you give it gas
where should that distributor hose be connected on a 460 ford with a 4180 carb?????
Which brand distributor is in the video?
Does the vac connect to the carb or intake?
hey man. ove your channel. I was hoping you. might have some insigt into some performance issues im having. i hsve an 82 GMC vandura. And just recently it started bogging down and losing power but usually just when it shifts into 3rd. I drove it with a vacuum guage attached to manifod vac and wn it bogs down the vacuum goes to around 5 and below. . could this bog be a vacuum issue? i have a vacuum advance on order as im pretty sure mine doesnt work. BUt i also think that it wasnt working for a long time. Also. I had an old timer mechanic convince me recently to bypass all my emissions stuff, and he unplugged all the hoses from my two TVS switches. Do those now need to be removed and plugged off? in other words...could they create a vaccuum leak if left in without any lines attached? im scratching my head for a wekk over this bog
My dad has a 66 F100 that I helped him swap a 390 from a 65 galaxy into. Has a mild cam, headers, Holley 600 and for some reason when the vacuum advance is plugged into manifold vacuum the truck dies. There are no vacuum leaks in the hose and the gaskets are all new. It will also idle only with part choke. Carbs been rebuilt twice. Any help is much appreciated.
What afr readings while vacuum advance is engaged?
How do you disable the vacuum advance altogether and then lock the timing in.
That's what stupid people do, but it's done by unplugging vacuum advance and wiring mechanical advance in place.
Great explanation for me. Thank You!
You invited questions so mine is: Do you have any knowledge to share concerning performance oriented centrifugal advance spring kits (for example Mr. Gasket 925D)? I'm running a mild 289 (F303 cam, Edelbrock Performer RPM heads, 650CFM Holley w/vacuum secondaries, headers, stock distributor w/Pertronix. Car is about 2400 pounds, 5 speed, 3.54 rear end. Thanks in advance.
Everyone makes ignition timing difficult, but it’s actually very easy.
Outside of your throttle settings, you want the spark to fire as soon as possible without timing creep at idle (too light of springs will sporadically pull idle timing)
So after you set your idle initial timing, choose springs that pull in timing as soon as possible without causing spark knock (pinging).
Set initial by setting your transfer slots tova square, and adjusting your initial timing along with your mix screws to set your idle - you have about 1 full turn of the idle screw from square t slot to play with before you get an overexposure scenario. I personally run on ported vacuum.
Typically I see that for most folks with vacuum canisters that pull more than ten degrees that this works best.
Thunderhead289
ThunderHead289 Thanks for the quick reply. And thanks for reminding me about possible idle creep. The good news is that light springs can possibly tailor the timing to an optimum curve; the bad news is the greater propensity for failure. And thanks for the Holley tip.
As odd as this sounds, I have found that I snap the heavy springs more!
Transfer slot theory works for all transfer slot carbs - with running a vacuum gauge and a wideband gauge side by side, I have seen the best results all that I have mentioned above.
Also, I super simplified this video - when you open your throttle, cylinder pressure also rises - the higher the pressure, the denser the mixture, and the quicker the fuel charge will burn.
So cruising needs more timing, into the throttle takes less.
Remember, the goal is to fire the mixture as soon as possible on the power stroke to use as much of that stroke as possible.
Great video! A carb tuning how to would be great
He has excellent videos on setting up Holley four barrels. OEM carbs are not tunable. If a problem has been reliably isolated to the carb it is either repair or, more likely, replace.
Where do you connect the hose?
Very good explanation.
Great video! I wanna know, why at full throttle, is manifold vacuum very low?
Because as you open the throttle plates, there is less restriction to the air flowing into the engine. That is why manifold vacuum is highest at idle, and lowest at wide open throttle.
Randy
Hey man I got one for ya! Okay, I just bought a 1984 f150 Custom short box 2wd with a 5.0 in it. And ive been doing a budget build on it and I just got my mad 6al box and my blaster 2 coil wires up and working, but now when I try and run my tach wire to the back of my factory tach from the tach output onthe msd box I get nothing. Now fyi this truck did not come stock with a tach, I robbed the cluster and wiring harness out of another junk truck and just wired it up to mine and it was working until the msd swap, now nothing. Help me out if you will!
Is vacuum advance only for carburetors?
I need know where the vaccum Gos to from the distributor
hi! Great video and thanks for the clear explanation. Am I understanding that correctly that a vacuum advance valve has absolutely nothing to do with a rough idles speed? I have tested the valve and the pin doesn't move at all while sucking the hose..I only can open it with a screw driver. I have a rough idle/bit revving too on my 1983 Honda Accord and can not find the source of the issue...thanks!
The diaphragm is probably damaged/deteriorated and has a vacuum leak. What will happen is if your engine is set at stock base timing is running retarded because it relies on the vacuum advance to run at its sweet spot. A quick fix is advancing the base timing to overcompensate for the lack of vacuum advance. Only problem is as explained here when you are at wide open throttle your timing would be more advanced than desire and you'll probably get loss of maximum potential power or pinging if it's advanced too far.
Seems to be that vacuum canister has a leak... those engines usually initial ignition timing is 6 bdtc with the vacuum advance disconnected.. if you have rough idle start by checking and tuning the basics, such as spark plugs gap, check condition of the spark plugs cables, the rotor and the cap also the right gap for the points in the distributor... assuming the carburetor has no internal leaks and it's in good conditions and valves are well calibrated
The guy who built my motor a 350 chev w/ RV cam. I told him I wanted low end torque sometimes it acted like it wanted to ping on acceleration. so sometime after I check where the timing was at idle and it was at 25 and also notice he had manifold vac not ported hoocked up so I change it to 10° initial timing vac disconnect and them hooked up to ported vac. What I noticed now is the centrifugal weights where sticking so fix that and now if I rev it quickly the idle does not come backs all the way down to about 750. I think he put in some really light springs so the weights start flying out just above idle. So I'm going to check it. and I got me a curb kit for the advance. Any thoughts on this will be appreciated. Yes I want good low end but also good mid range. Someone on u tube said he likes having total advance by 2400. What do you think?
What vehicle is this engine in? So-called "RV" cams are typically low duration, low overlap designs that build a lot of low end torque and flatten out above 4500 rpm. Cylinder pressure off idle is high so they don't need a fast timing curve with a lot of advance down low. Full advance by 2400 may be ok for a light performance car with short gears and a performance cam but is too early for a torque motor in a heavier vehicle as it would make it prone to preignition. Total mechanical advance of around 36 degrees is good but I would think having it all in by around 3000 would be safer.
@@65sohc 68 chec truck 1/2ton manual trany 3:73 gears w/ 31" tires
Its a 4x4... i know twilight zone moment where's Rod Serling???
@@65sohc total timing is 69° 15 ° above normal i know. Harmonic balancer is in good cond. I think its the 8° of advance valve timing that he set that causes the ing timing to have to be 15° advanced. Ro run right. No pinging either.
@@mtnman6278 Have you actually checked the timing yourself? 69 degrees seems impossible. If I'm not mistaken advancing the cam creates even more low rpm cylinder pressure and wouldn't call for more ignition advance. But if it runs good what the heck.
If you figure vacuum advance is about 15 degrees+centrifugal 25, that's 40. In order to have 69 total initial would have to be 29. I'm surprised the engine would even start with that much initial timing. Something isn't right. If those are actually the numbers you are seeing on your timing light I would suspect the marks on the balancer are off.
So I know this was two years ago but my girlfriend has an 82 GMC sierra s15 and we can not figure out where to attach the vacuum hose to the carb... any suggestions on which carb port it is?
Most carbs have a full time vacuum port and another that supplies vacuum over about 1000-1200 rpm or thereabouts. I've always found I got better results using the full time port (usually lower down on the carb). This was with both small and big block Chevy engines with headers and mild aftermarket cams in fairly light cars. I got much crisper throttle response and the side benefit of slightly better gas mileage. Your engine/vehicle combination my prefer the ported vacuum (usually higher up on the carb). Why not try each for a day or two of normal driving and see which you find better?
Just be sure to block of any unused ports.
Let me know your results if you would.
my car has a distributor, ut it has two vacuum lines. please may I know where to fix those two vacuum lines the carburetor
I bought a 70 Impala with a lot of stuff wrong with it. Got most of the major things fixed, but I'm having a hard time knowing where to put my vacuum hose from valves to the 2 bbl carb. Bought a Haynes manual and that was pretty useless and I can't find any stock photos of a 69 or 70 with the air cleaner off. I just want it to run right. Not fast
SwitchDoctor it goes straight from the distributor to the front pass. side port on the carb.
Borrow or buy (Harbor Freight has decent cheap ones) a vacuum gauge, connect it to a port, test if it has vacuum (needle is up at idle) and when you rev the engine the needle should drop (no vacuum). If you connect it to a port that does that you should be good.
Lance Uppercut woo wait. mine is the opposite.. idle no vac. half throttle 15 in. gm hei .
@@danwells7691 If you have no vacuum at idle and then vacuum starts as soon as you open the throttle a bit that is ported vacuum.If you then punch the throttle vacuum should instantly go to 0.
Question: Just completed tune-up on 318 Mopar Engine 2 barrel Holley; idles and revs great until I hookup vacuum advance; starts missing when reving RPMs; What's the problem? Remove vacuum advance and runs great again!?
Either the vacuum advance is adding too much timing (likely) or the vacuum advance diaphragm is ruptured and causing a vacuum leak (unlikely).
Another great video...very informative.
Can too much timing cause me to stumble than take off when I mash the peddle ? Throttle response is really good with regular driving. But if I go from idle to (wot) it falls on its face than takes off like crazy ? Would you call timing or bigger square nozzle ? I have a summit carb. Running manifold vacuum on stock cam. 12 degrees initial timing.
Timing that works is a reflection of your idle mixture. - they both work hand in hand. It sounds more like your transfer slots may be over exposed at idle which are in charge of some of the off idle transition. Also, make sure you don’t have play in your accelerator pump. That can easily cause a bog off the line
Too much timing you will hear the pistons pinging.
I have a small block chevy and car runs when vacuume advance is unhooked but car dies and back fires when I hook it up can u tell me what would cause that....
The first thing that comes to mind is that that vacuum advance diaphragm is ruptured. When you connect it you are introducing a big vacuum leak.
Hey dude, sooo... I have a wrangler with a 383 stroker 220cc heads, big mutha thumpr cam and a Holley hp street 750 carb. The thing is that it takes like 6-8 trys for the engine to run, it turns and then it feels like it chokes and dies. The mechanic told me that it was because the engine is cold but I have seen engines like mine on UA-cam that turn on right away. Also, it feels rough under load. Do you think the distributor has something to do with it ? The total timing is at 38 I was told, 15 initial timing and I can’t remember the other one.
Was this setup on a dyno?
Your Heads are too many CC's and a mutha thumper is a botique cam designed primarily for a lopey idle, and not performance. Next time call Chet Herbert cams and tell them your parts/goals and they will grind you a cam that makes much more power. You can use heads that big or bigger in a drag race setup, but for the street/woods you would be better with smaller heads. Even down the 180 cc runners This increases velocity and low end torque. What you want in a Wrangler.
Don Rutter the main purpose of the Jeep is sand drags not rock crawling. I put that cam because I had it from I project that I was going to do but I never finished it and I sold it. And the heads are 220cc CNC ported.. sorry for the typo.
I have a really dumb question.... my vacuum advance hose is missing from my distributor. If i re-attach it, does it plug into my carburetor?? I just got my 73 Charger back on the road after 4 years of slumber. She's running hot, and my idle is funky. I have an 850 CFM Holley double pump carburetor. Where do i plug it in? Im a female gear head, and I work on the car myself, but this is a new one for me... Im kind of embarrassed to ask...
It would help to know some more details about your engine. That is a lot of carburetor for anything built in 73. That engine would originally have used ported vacuum which does not affect idle quality. Therefore it would be important to know why the idle is "funky" and, just as importantly, what you consider funky. Thunder 289's Galaxie has a rough idle, owing to the camshaft overlap, but it sounds anything but funky. To answer your question, your 850 has a vacuum port on the side of the primary metering block that is used for vacuum advance. Base timing needs to be set first.
Bottom of carb is manifold vacuum, right side of carb front bowl is ported vacuum. Use manifold vacuum. You arent worried about emissions (ported) you want it to run good, and not hot (ported). The Duntov cammed 64' corvette was the first to use ported vacuum, GM engineers admitted it was a mistake, engineers say all motors with ported distributor vaccum were an attempt to meet emissions, and the motors run hotter. Ported vacuum is another abomination you can thank the state of California for.
If I am understanding correctly, I plug the vac hose when I am setting my initial and the advance timing. If I have an aggressive cam (280 degree intake/286 degree exhaust), I use manifold vac, or ported vac?
Manifold. And any cam around 300 degrees or over you definitely dont use any vacuum advance. Bigger cams, you set the timing somewhere in the 16-24 degree range at idle, and build a stop on your centrifigul advance to full advance at 36. Big cams need a lot of initial timing. Bigger cams need the most. They dont make enough vacuum to run a vacuum advance properly. The low vacuum causes "dithering" that means the vacuum cant open the centrifigul advance all the way, so it never ends up at the same spot at idle, causing erratic idle RPM's and stalling. Older cast iron heads have poor volumetric efficiency so need the most timing advance compared to modern computer designed aluminum heads. The more duration you have (valves open longer) the bigger the pistons you need. Valves open longer steal compression.
Always ported vacuum.
It can go both ways.. If you are running very rich, it will slow the burn rate. If you are running very lean, it can increase the burn rate.
i agree with you - but only in excessive scenarios. a rich mixture that is too rich cannot be properly ignited, a lean mixture will get extremely hot from the compression and want to preignite. if either of these scenarios (below 10:1 or above 14.5:1) exist, the carb needs to be adjusted immediately or permanent damage can and will occur.
I have a 69 Skylark Buick L77 350 4B 10:25:1 compression.. 285hp 400 ft lbs.. It pings. I have it at 4 degrees static. I run super 91. Under low RPM and a good load, it will ping. I can get it to stop by going 2 degrees static.. But I lose so much power. When the motor is cold and warming up, no ping. Once it is warmed up.. Some pinging.. Any suggestions?
what carb, intake, and cam style are you running? also, what is your elevation and relative driving temps? and when you say static, do you mean initial timing BTDC? are you using a timing light to determine your settings?
Quadrajet . Engine is factory original. and yes.. BTDC. I am at 6000 feet. 9000 feet for HP reason as we run at times single digit humidity here in Colorado. Yes.. I use timing lights. Temps here as of late are 70 F. Normally I run 1.5 degrees advanced for every 1000 feet. But on this Buick, i can not do it. Must be because of its high compression as it was made to burn Ethyl pump gas back in the 60's. I am considering a 4 row aluminum radiator and a 165 thermostat.
well, i cant chalk it up to too lean of mixture as you are lacking oxygen at those levels to the point that you may have to even pull jet out of it. im curious what your plugs look like - you seem very competent in these affairs.
the lower you can keep the engine temp (dont operate below 160) the cooler the cumbustion chambers, and the better they will resist preignition.
let me know on the plugs.
Great explanation - thanks for sharing!
No problem, glad it was informative
Thanks I found out why my carb was backfiring under load with a bad diaphragm
What does the vacumm advance connect to?
Hi from Venice Beach. .....How do I know how much vacuum my vacuum cannister is rated at.?
The only way to know for sure is to connect a timing light. Check timing with vacuum advance disconnected, then with it connected at full vacuum. To get full vacuum at idle and thus max out your vacuum cannister you will likely need to use either a vacuum pump, such as Mighty Vac, or suck on the hose like Thunderhead289 did.
You need to go to the NAPA listings. There are MANY vacuum advance units for different applications (same motor different years).
what would you recomend for totel timing on a 1979 351w 2150 motor craft 2bbl c4 trans chines short tube fox body headers duel 2.5 exhaust h pipe glass packs no smog junk on 87 octane?
32, then 34, then 35 deg. @ 2,500 rpm. Test drive at each. Choose whichever one performs best at that point. Just saying.
I have a question my car feels like its ristricted like to only go 45 miles an hour its a 235 engine i have a stainles metal line from the carb to the advance. .so my friends say the line is to thick its a 1/4 line they say the line restricks the distributor from turnning more so the car can go faster is that true .. I hope I make sence please any one let me know
Can you make a video on how to adjust and set adjustable vacuum advance. Thanks
Gregory Frost - I just follow the directions on the box. If you turn it counter clickwise to start then with the allen wrench turn it in until it just stops. Then hook the lvacuum line back up. with the engine warm take it up on the freeway or a deserted road and at cruising speed start to accelerate and try to detect any pinging.
If not, then keep backing the vacuum advance out 1 turn and rehook up the vacuum line then take it for a spin listening for any pinging. So you keep doing this until the motor pings. When it does then go back and turn the vacuum can in a turn. Then hook up your vacuum line and you should be set.
Don S Thanks for the help
Do you have to plug both end ? At the vacuum and carb?
Only need to plug carb. Canister gets no vac without being hooked to a source (carb)
So if you run ported you don’t use manifold vacuum??
This is an old video where I taught along conventional lines - I have since said heck all that and teach how I do things because honestly conventional carb teaching sucks and doesn’t perform as well
I have a 1972 chevy C-10 pick-up, it's been rebuilt with a RV cam in it. but what's it's doing noiw is, when I coming to a stop sign or a stop light it dies on and someone says it might be my vacuum advance or air leak in one of my vacuum lines.
how do you have the carb set up?
sounds to me like a carburetor issue. i have a wealth of videos on carb tuning, but i can try to direct you here
Same problem ... have you fount a fix yet?
Set timing to 36 degrees total, restrict vac advance to only 10-15 degrees and plug into manifold vacuum. Check for vacuum leaks in the hoses and the carb base. What carb do you have?
Spray carb cleaner or brakleen around the motor areas with it running (not around air going in carb). RPM's rise at a vacuum leak.
One engineering point.
People think the fuel/air charge explodes to drive the piston down. That is incorrect.
The fuel/air charge burns across the cylinder from the spark plug to the far end of the chamber over a few milliseconds to build needed pressure.
What is not mentioned is that max cylinder pressure is needed at 10° ATDC for maximum leverage.
Mechanical and vacuum advance are used to build the needed pressure at all speeds and loads.
Question .. my Cleveland 351 bored 30 mild cam stock crank , 650 edlebrock my little prob is when iam at cruising with very pressure on the pedal I get a pop through the exhaust it happens in 3 rd and 4 gear . Just thought I would pick your brain .. thanks
seems like too much cruising ignition timing off hand. several things can play into this including air fuel ratio. if you have vacuum advance, remove it and see if the issue persists - this will help diagnose the problem. get back with me here.
Thanks ,will do
Well I remove the vacuum advance hose , plugged off both ports one on carb other distributer and problem gone , can the advance be changed or adjusted because the vacuum advance can be tuned with a Allen key
ah , good deal. so it was bringing in too much advance. the adjustable units are a bit tricky. if you lesson their advance, you will also lower the vacuum at which they will drop out of the timing equation. so for example, you have one pulling in 15 degrees of timing that drops out at 13 inches of vacuum. adjusting it will make it add in only say 10 degrees, but now it drops out at 10 inches of vacuum. my issue is that they are still adding in extra timing now at a higher load then they were before. its just gray area. this is the point where you have to listen for pinging or stumbling issues.
Well in the gray area , there is no ping or stumbling . Now is it possible to adjust the timing so I can run with the advance hooked up to improve fuel economy and easier starting ( just that when the advance was hooked up the choked worked , one press on the pedal and it fired up and run on high idle then when warm it kicked down)
Well explained, much appreciated!
glad it was helpful
thanks for all the videos, you have helped many times. I have a 302 out of an explorer with a light cam, i was having issues trying to get on it high rpm, i installed fitech, same problem, so i added pcv, got better then all the sudden an afterfire and now its rough low rpm.. someone said i might need to add vaccum?? maybe vaccum canister?
also i do not have vaccum advance
Spray for vacuum leaks first.