You sir have answered a lot of questions I had about upgrading to a bigger carb and informed info's I never knew I needed. Big thanks. Your channel is great.
I went from 24mm to 32mm flat slide with upgraded 7mm lift cam. The engine is 200cc single cylinder pushrod type. It runs good. Though sometimes there's a little bog on mid throttle and sometimes the idle is not stable. I'm thinking that it could be a faulty needle. But its true, at high RPM, it runs like a beast, and its a lot of fun. At low RPM, it pulls like a champ as well. Its just that mid throttle and idle that bothers me sometimes.
It you find that lifting off the throttle makes it try to go, its running weak in that area. or rich if you get nothing from lifting. Mid range, try lifting the needle by lowering the clip if it has one.
Roundslides seem to be easier to tune same diameter i ran a flatslide 30 on my 150 changed it to a nibbi 30mm ran way better for some reason if u run pwks they dont seem to run how u want them on a 4 stroke
Got a 4 valve zs212cc and I got a 500 dollar proper motorbike carby I wanna use ids 33mm how would I make this work on a 28mm/30mm manifold any help be appreciated thank you ??
I was confused about the decision to buy "Mikuni VM Series Carburetors VM26-8074" or " Mikuni TM Series Carburetors VM28-418" for my Yamaha Rx100 which has an oversize imported piston, but I'm clear now thanks to Junkman for the crisp and easy explanation, I'm going with 26mm.!
I have a standard 135cc motorcycle using a 25mm carburetor. I upgraded it to 150cc with some other upgrade such as racing camshaft, high-compression piston, bigger valve, K&N round air filter, leovince exhaust... and I used a 30mm CV carb , it works ok with good performance. And then I kept the 150cc bore and downgraded to standard camshaft, lower comprestion piston, smaller valve and original exhaust, stock air box filter, but I kept the 30mm CV carb and it didn't work well even though I tried to adjust it. And I replaced the 25mm carburetor and it worked great.
Great video! I have a small 125cc Suzuki (Address 125/FL125/Shogun125, various names in different areas). Since the EFI unit went bad (costs like 300-350 euros to get a new one), I went with the good old way. Converted to carburetor (the Asian version comes with a 18mm Mikuni VM) and used a Keihin PZ 18mm one. Engine had good low-end torque but lacked power on the top-end. Meanwhile, I had literally zero experiance with carburetors. Stupid me, went on to get an OKO PWK26...I tried different jets (32,34,36,37....105,110,115,125...) but still the bike couldn't keep itself idling for more than a minute. Low-end the engine was like "choking", top end power was good but I felt like it was lacking something. After about 2 weeks of torture with the OKO, I sold it and got a 22mm one. To my surprise the bike runs great! Didn't have to get into jetting, only had to adjust the idle speed a bit. Both low-end and top-end is good and even in cold temperatures, the choke works well so far.
Yes. And this video is part of a larger series on carburetors in general. I have an entire page on my website dedicated to all information centered around carburetors and tuning.
If the carb is a 30mm and the port or opening in the head is 24mm you create a bunch of turbulence in the flow. you might be able to make the bike run but that trubulence can make it hyper-finky to tune and then you have to get into the other things like cams and valve diameters and exhaust and and and.. but the first step should always be matching the carb to the port.
I guess it all comes down to the idle and max rpm’s mandatory cfm “cubic feet per minute “ of air. And the carburetor must be able to perform at both ends of those requirements. The inability to do so will starve the engine for fuel or flood it with too much fuel in the air to fuel mixture.
@@booz8313 i can respect that. Currently running a 80cc derbi with a 28mm as well. The thing rips so much you can hear it sucking all the air in. It's crazy b
Glad i found this video I went from a smaller carb like the one in the video and i got a new one same as the bigger one in this video and I cannot get my bike to start now
There’s no solid formula for the ratio of carb size to capacity especially since multiple different engines of the same cc can use vastly different carb sizes
Maybe u gotta try each size, but thats gonna costs a lil bit In my case im using 30mm carb on my bike, but the performance only good starting middle rpm to high rpm. Low rpm quite poor performance, it feels heavy. I need to downgrade to 28mm carb to get good at low rpm. Since im using it for daily. Unless im going for touring, then i would use 30mm back.
you have to measure the ports and that determines what size carb you get and the most you can get out of it like it determines the biggest one you can get for your bike
I just wanna run this f7. Bad 26mm carb missing everything inside. Now i need to dig around and see what carbs i have around here. I know i have a brand new 24mm mikuni. Its too small but atleast now i know ill have tons of low end power to put-put around in the corn field
on my snorkeled 4wheeler i used pvc no air box just a boot i have a ball valve on the stack to change the air flow if it is all the way open it bogs at wot i close it about 1/4 way to tune top end works for me 30 mm carb 230 cc quadrunner
I have a klx 143 v1 head it's a trail bike I believe same with the 26mm carb its cold here but I put a bigger jet and dropped the clip to the bottom plug is dark and oily I'm going to get some fatter jets and play around more
I got a 28mm PWK for my 86cc 2 stroke Suzuki K50 moped, peak power between 8-10krpm and runs great, guestimate around 15hp and a bit more to gain with some optimizing work on the channels in the engine block and such. 24mm on my 280cc trials bike, but it can tow a car from idle. Ordered a 32mm for my Suzuki GP125, aiming for a peak power between 10-12krpm.
all you have to do is measure the diameter of the port on the head and match that to the closest size carb available anything larger will just hurt performance. for instance the port on my lifan 125cc measured roughly 19mm, so that is the size i went with over the stock carb that measured 16mm, after proper jetting was night and day on the mid to topend. i see so many running anywhere from 22-28mm carbs and unless you port the head on 4stroke or cylinder on a 2stroke to match the larger diameter it does nothing but hurt engine performance and becomes a bear to tune if at all possible.
Thank you for this video I understand it a little more. I have a 150cc scooter that I upgraded to a 211cc. 63mm bore 10.2 stroker. I've notice when I have my 30mm cvk pumper carb great throttle response and top end. So I switch to a 32mm slide and not so great take off its okay but my top end is great. Should I switch to a 30mm slide carb
I have a brand new 230cc 4stroke dirt bike with a 28mm carb, I cannot seem to eliminate the idle to wide open bog, and it falls on its face type of bog not just a slight hesitation... any ideas? I have tried so many settings and jets with it to no avail?
Are 24mn flatslide carb almost equal to 26-28mm round slide carb at full throttle opening? Because of the poor Flow in the round slide carbs at full throttle? Faster airflow/velocity in flatslide and chainsaw carbs then round slide carbs? 🧐
Just a question, how to determine which main jet size is to be used on a certain carburetor? For example, what size of main jet should i use for a 27mm carburetor round slide?
After ordering a carburetor from China, I am still trying adjustment and it was advertised as ( fits DS80). I have the engine bored and ported. The engine also has a high flow exhaust. It is likely that going back to a stock carburetor is best.
Okay o find this funny I have a 30mm pwk carb on a 50cc! And it runs great it idles better than ever. it rides smooth. But remember my stock carb was a 17mm carb
He is saying absolutely right i have tried on my 150cc bike with 30mm while its stock is 26mm. Bike pick increase but idling not get tune. Now i am using 26mm pz26 its give good acceleration and idling is also f9. Further i have order some other number pilot jets from which i can get more batter idling. But plz search any calculation about this thing which make easy to chose carburetor and there jet for best performance at any level?
I have a 200cc scooter that I changed the carburetor to a 30mm and it'll start,idle,and drive in the low rpms but past about quarter throttle it bogs down and starts popping..... Any suggestions on the jetting or adjustments that I can make to get those about quarter throttle rpms???
Is it bad idea to replace CV carburetor to a slide one in a 450cc dual cylinder chopper? what are the cons? hard to find a cv one for reasonable price..
My dad left me some variaant of a Homelite Super XL from the 1970s. When it runs it has tons of torque and cuts great. But it hasn't run well in years. Probably the biggest issue is the carb. These carbs have a 90 degree inlet fitting that make it very difficult to work on. I've seen tillotson carbs that should fit that don't have that 90 fitting. All I have to do is drill a different hole in the side of the cover and I'm good to go. But which Tillotson carb to choose?
Is there a ratio for engine size to carburettor I have a royal Enfield classic 500 which is a long stroke thumper with a 33 mm carb and I have other smaller 200 cc bikes with the same size my plan is to upgrade the 500 to a 42 mm carb with a longer manifold to get better mixing of the gas and adjust the cam timing for rpm will it work or will it stutter midrange I did the same on a custom 200 wher I over bored the engine from 160 cc to 200 it had issues with mixing the fuel past 4000 rmp
It would be nice if it were as simple as Displacement : Carb size, but there are too many factors in that affect what the engine requires as far as carburation is concerned. I may do a future LIVE Q/A and go over this as it is a lengthy explanation that ends with a "it depends". For you it is largely going to be a trial and error process to get a carburetor sizing and jetting dialed in given the modifications you plan to make.
Your camshaft documentation should give you some guidelines on the size. It will also depend on your intake manifold. Something like a 500-650 cfm should be just right.
I have a Chinese cool strip 125CC and it has PZ19 stock carb on it. Is there any point in putting a 24 or 26 mm carb on it then would I have to get an intake Adapter boot? Do I have the wrong thinking about this whole deal?I just want the bike to idle and run better these carbs I keep buying for For 18 to $30 just don't seem to be doing Right and definitely not very long.
Hi God bless you and your family I have a yamaha yz 85 02 I would like to nkow from you what would be a better carb for my bike than the stock one please let me 3
If you measure the slide on the left carburetor,you will notice that the slide will be narrower than the opening going to the engine(around to 20mm). This is the reference i take in mind in order to measure, because the air will always have the speed of the narrowest point on the whole intake. Am i wrong here?
Hi Junkman. I have a project bike a 78 dt400. It has a 34mm round slide. I would like to try a 36 mm flat slide carb. I was wondering if for a given size round slide vs. flat side mikuni carb is the float tower talker in the flat slide. I have limited clearance above my stock 34mm round slide as the pipe crosses above it.
Hey me I got a 2 stroke blaster I cleaned the original carb still over flowed ajusted the needle still over flowed bought a new stock crab put it on and same thing it over flowed I don’t know what to do at this point and all the shops around me are booth
I have 1 motorcycle 2 stroke at the same time my standard bore stroke are 57mmX54mm.my question,what size bore or piston i need to use carburetor size 58mm for dragrace?
the stock carburetor will be fine, just re-jet as necessary. However if you have a CV type a change to a piston or mechanical slide type would be preferable. See my other videos on that. ua-cam.com/video/i6yOd2lwwDU/v-deo.html&t
mr. junkman got an 05 yamaha venture took off each side breather and replaced with pods took off all emission stuff runs ok but lost a little snap and alot of top end opened up mixer screw 1/4 turn for more fuel didn't make much difference any suggestions. thank you.
I have a problem with this tool, it's a KTM 250 2T The tool has not been used for almost a year This week I found time to take care of it, I did a fuel-oil change, I cleaned the filter plug, everything, finally I tried to start it, but the car could not start. It only started with carburetor spray and shut off straight away From that I understood that the carburetor needed to be cleaned and that's how I did it. Now the problem is different, the motorcycle drives straight up to very, very high turns I played with the air-fuel screw but unfortunately it didn't help. Is there a situation where the problem is different? Something in the carburetor maybe? need help please
I built a 2018 honda 250x 4wheeler for my nephew with a high compression piston, opened up exhaust, opened air box and jetted carb. I was surprised to see it came with only a 20mm carb being a 229cc with around 18hp stock. Would I gain anything from a bigger carb?? I can't find an example anywhere of anyone putting a bigger carb on one of these. Seeing that most 125-140cc engines come with a 20-22mm carb and even the 6hp go karts run that or bigger makes me think that these are undersized and maybe I could gain a lot from a 28mm or so?? Any advice would be appreciated!
Question. On a 125 honda cm twin with pod filter and slightly modified exhaust, comes from stock with a 26 mm carb. Would you recommend go higher on main jet or go to a pz30 and decrease main jet size? Thanks
just discovered your vids today and immediately had to subscribe. i wish these vids were on youtube when i was learning about carbs few years back in my carb scooter days. you do a great job and insert great illustrations. this particular vid is beyond what i need, i was just curious, but i expected something like: for single cylinder 4t 125cc you use this big carb, for 2t 125cc single you use this, for 4t 250cc single you use this, for 4t 500cc twin you use this, for 4t 883cc twin you use this carb if your cylinders share one carb, but you'd use these two carbs if each cylinder is fed by their own carb... catch my drift? Again, i love your vids and am leaving likes as much as i can.
I or anybody else can't say exactly what carbs one should use for a given engine displacement. Not every 125 4T engine is created equal so what works here won't be the best for over there. Some general rules apply but it relies so heavily on the volumetric efficiency that is built into the design.
Just saw your vid. My question is the bike I juts got, 2 stoke 250cc (actually like 229c) came with a 38mm carb. Kinda seems too big. The pipe Is a smaller pipe for a 125ccbike. I will be putting on a larger pipe however. So should I stay with the 38mm? It took me a while to get the bike to run without bogging when fast throttling but just not sure if I should go down a size or keep it due to pipe change soon.
2 strokes require a matched pipe for proper operation. Your bike might need crank seals if it is old or worn. Same if this has reed valves or some type of exhaust valve.
Had the same problem on my 70cc bike i went to a 21mm from a 12mm it ran but was so rich it's soaked the matting in my pipe then the bike got to the point where it wouldn't even run I went back to the 12 mm bike runs perfect lots of low-end torque but just like you said I lost top end
I just got a new carb for my motorized bike but I couldn't get it tuned right the idol was simply way too high and it wasn't really responding to the throttle. I think the jet size might be too big for the engine?
Greetings junkman. I just bought a 2 stroke motorcycle. The previous owner told me he has change the cylinder bore and piston from 56mm to 57mm. Is it necessary for me to change the 20mm carburetor to larger carburetor seems the displacement has change from 120cc to 125cc.🤔 Thanks.🙏🏾
Generally speaking all the components need to reflect the rpm range that power is desired. Bigger is only better if the power is desired at a higher rpm and cam,exhaust etc need to reflect that. Even then there is a saying in motorpsorts, that horsepower sells engines, but torque wins races.
What is symptom of too big of carburator? Hard starting? I have a tpr 86cc 2 stroke with 30mm flat pwk polini with vforce3 reeda on a yamaha zuma. It is alwyas hard to cold start it. Once it started, starting is no problem,idle is perfect, it rips too on all throttle range.. It is just the starting that i am having trouble with. It basically floods my exhaust maybe around 10kicks with 1/2 throttle before it even start. Choke doesnt do nothing. I have highher chance of starting it with pulled throttle up to 1/2. Thanks!!
But if I wanted to go one single carb on a 77 CB750 F2/3, I would use a 4-1 manifold witha 34mm Mikuni carb? I know I would have to mess with different jets. Any help?
Please respond!!! I don't want to blow up my engine again I have a 96 Polaris XLT special with a 580 monoblock comes with 38 mm mikuni's the sled I am currently building had 34 mm mikuni's I took the 38s and put them on the sled I'm riding that had 34s is this going to be okay the other day I blew up the original engine that had the 34s on it had to pull another engine from a different sled out back that had 34s on it that's the one I put the 38s on sorry about the long comment but I don't want to seize another engine this one has awesome compression
There are more factors than carburation at play when an engine seizes. So that might have not been the issue. If you are worried start off with a bit richer fuel mixture, test, then fine tune the jetting leaner doing plug inspections regularly. And if that sled uses oil injection be sure the system is blead properly.
great video! hope you can help me with this issue. I have a dual-carb yamaha virago 535 (1994) and I want to convert to single-carb. Since each of the stock dual carburetors has 34mm, which size should i consider for the single-carburetor conversion? the same size? or do I need to compensate with inside jets? what is your advice? thanks in advance!
Cool video, so what if you had say a Keihin Pb18 and the Mikuni equivalent.....they would still have slightly different attributes? Like more adjustability of each circuit?
question, i know its odd that a certified master mechanic should know this, but i was given a nibbi racing 24mm output dia with a larger 35mm intake dia as my OEM carb. oem carb is a 33 input, 30 output. nibbi is a 35 input, 24 output. id assume that this carb would lack airflow if i were to boot it to my 250cc 4 stroke's intake. I dont want to lean my engine, I'm okay with a small loss of power, shes an in town putt-round anyway, but more low throttle power is desireable. ive never asked the question, cam i down size my carb and not suffer too many losses, maybe even experience some gains in fuel economy.
Hey, new subscriber here! I also have a 125cc, changed the block/piston to 56mm now its a 135cc, same deal im using a 28mm carb, regrind cams, intake and exhaust ports are ported and polished(which some people said were too big), big valves, free flow exhaust. with all these mods i only gained little power and it is so hard to tune. So Watching ur video convinced me or made me suspect that my carb is too big for my engine. I also heard that bigger intake ports could lower velocity. Do you think reducing the size of the intake ports could increase power or atleast increase velocity of the air fuel flow? Or should I get bigger cams to compensate with the big carb and ports? What are your suggestions?
It depends on what you want to achieve. Re shaping ports is not an amateur job, especially if you are trying to optimize flow characteristics. I would make sure you have a cam that has enough duration and overlap to keep the air moving and fuel atomized.
i just recently did the same thing got a whole new top end bigger piston to a 56mm which stock is 52 on the 125cc same thing i got valves done 7.0 camshaft and a 28 mm carb should be perfect for the bike try getting more performance stuff to help the tunes more like get a different cdi box different coil for the bike that’s what i did helps with better timing and stuff and get all the power you really want in the bike i had got a 30 mm it works but i feel like going down to a 28 it’s way better and should be perfect
@@thejunkman great video brother, do keep up the good work...I have a quick question for you concerning cvk carb vs the slide type , I have a Honda storm 125 cc and I have noticed that ever since I bought it brand new ,the start up is ok but sluggish when accelerating, I've noticed the same thing with guys who have the same type of bike , after research I've found that the diaphragm type carbs are much slower in reaction to the slide type ...my question is is there anything that can be done to improve the throttle lag and also can I swap out the cvk for a mikuni , if so what size do I purchase and what else do for the mikuni to work? Thanks in advance
@@deniscastro2880 problem here in Philippines their is alot of 2 stoke dirt bikes running around in 125cc and the 28mm works ok with reeds, not so with 4 stokes.
Too big of carburetor on a 2 stroke will reduce peak,it won't reach peak rpm,if you have a 100cc 2 stroke with ported intake and exhaust i recommend putting 24-26 mm carburetor,too big of carburetor will have large fuel droplets meaning it will burn slower,smaller carburetor will have more intake velocity making guving a better atomization and wuicker burn rate
i have a question i have a wave 125 with 57mm block and i want to change to big valve head and im choosing between 28/24mm head or 31/27mm head some mechanics says that 28/24mm head is better to use on 57mm block than 31/27mm head...i dont understand why 28/24 is better than 31/27 head..is the bigger the valve are better right? ineed your help
In some cases bigger valves mean a slower velocity of the air moving in or out. This typically means less low end torque. However, larger valves are better if the engine sees mostly high rpm use. Some where in the middle is the sweet spot. This is probably why the recommendations are for the smaller valve combination. You will need a cam to match this new configuration though.
@@thejunkman how much camshaft lift should i use 6.0 or 6.5 because im planning to have my wave to be drag racing setup should i use large or the right size of valve my current setup now on my wave 125 is 1.57mm big bore kit 2.6.0 camshaft 3.advance ignition timing 4.high compression 5.24mm flatslide carb 6.stock head 24/21mm 7.racing clutch spring what other things could you recommend to me to make my wave 125 more powerful im also planning to get bigger valves and larger carburetor but what size i want to use my wave 125 to be drag racing type btw the stock block of wave 125 is 52mm thanks for replying to my comment😊
i cant find any info about the lift of the cam but aftermarket racing cam you can buy is ranging from 5.3 lift to 7.3 lift maybe the stock cam lift is somewhere between 5.0 to 5.3 idk
It will probably work from a design standpoint, however it probably will not bolt up being the mounting points and cylinder port is in a different place so the bends won't make it physically fit.
I threw a 26mm on my powerfist 208cc (go kart,mini bike, woodchipper engine ect) has a 3 stage header, removed governor, fuel pump normal stuff. The stock carb was maybe a or 20mm or so an man its a huge difference lmao
Great video, I have a kz400 with no carb, would it be possible to use a similar sized carb from a Honda, Suzuki or Yamaha, I would have to get it to fit correctly, of course.. thx
What year? To a certain extent yes, but there will be an experimentation period to get the jetting right. The first year used different carbs than later years. I have a 1974 that I restored and then 2 later versions for parts.
@@thejunkman it's a 1976 I believe, once I get out of storage I'm going to try a gs450 carb I picked up for $10, not much to lose for that price, I'll check through your videos, I have much to learn
The carb I have is I think a 27mm, and I found a much better looking 33mm, Thoughts? The engine is a 44ci briggs vtwin, the oem carb has all of one adjustment, Idle speed... The one Im looking at is from an Yamaha Raptor 660.
I need your help please. I installed a two mm larger flat slide pwk oko carb on a ktm 50cc, air cooled, case reed w an 80cc exp. chamber. Being 2 mm larger w a graduated (coned) intake, what jet size, pilot should I use? Im pretty certain the stock jet on the stock 19 mm carb(round slide kehein) was a 105-108. werent marked? I compared to dozens under a mag. glass.
junkman. hope you can enlighten me. a 150cc (62.2mm x48.8mm) DOHC engine, so it certainly lives at the top rpm..peak torque and hp between 8500-9500rpm i think, stock camshaft .. comes with a standard CV carb 26mm.. is 28mm a good upgrade or 30mm? if im opting for 30mm should i change the camshafts at least? what kind of modifications you would suggest for this engine for a higher top end?
What about the venturi size? I was told that is the real size of the carb. For an example, pitbike engine 85cc, 70cc cilinder head. inlet of the Cilinder head is 22mm, and the inlet valve is also 22mm. So it needs an 22mm, I have a vm22 carb, manifold size is 26,(i made the inlet bigger to 26mm with an Dremel). Whats your opinion on this?
Well doing what you did will benefit the top end, but sacrifice the lower end torque because the larger opening reduces the velocity of the incoming air.
22mm venturi size. Now just to be clear, 26mm is a pretty big jump. This engine might just fall on its face at low RPM's and it might be hard to jet for the low/mid range without some issues.
Hello what would be your recomendation on a 150cc with a full system on also Racing CDI, Coils and spark plug and a couple more mods, I’m trying to reach the maximum performance out of it. I’m looking between a Nibbi PWK26mm or PWK28mm which one should you recommend? My stock carburetor it’s a Pz27 which measures 27mm on the cylinder side! Thanks a lot sir I would really really appreciate your thoughts on this matters since I’m new to it
So, if I want to put dual carbs on my I4 honda cb750, how do I pick my carbs, Murray dual carb kit has two vm34, but I don't know how much modification was made to the carb. Any tips? Does the size of the 2 carbs need to be bigger to compensate somehow?
I have a twin cylinder Honda CD125 Twin Bike with CB points and a 6V system. My engine is running smoothly and with more pulling power at cold weather, Early in the morning and at night. But when I ride during the day when the atmosphere is hotter then the engine is not running smoothly and the engine power is lower with increased engine noise and engine vibration. When I happen to ride from hot atmosphere into cold atmosphere due to raining on the road immediately the engine is begining to run smoothly with less engine noise, with less engine vibration and increased engine power. I wanted the engine always run smoothly as It was in the early days that bought it. On this matter I had many technicians try their skills on my bike and non of them were so far able to solve my problem and bring the engine back to the performance at early days. I am still wondering what could the reason be. Hope to have an efficient answer and advises to regain my engine performances. Thank you in advance....
Hi. I have recently developed a hobby of putting carburetors on non-carbureted engines. Currently I am running a Honda D15B (1493cc 16 valve) with a VW 30/31 (designed for 8 valve 1600cc). It runs great and I am super proud. However, I am flirting with the idea of creating a dual carb manifold. Do you think would be able to run a 2 VW carbs with only some minor adjustments? I feel like it would either *just work* or I would run into a rich condition. I cant find a guide online, do you have any incite? Thanks :)
I have a superstomp 125 (chinese), completely stock. It bogs down in high revs but iv checked the carb and the jets are squeeky clean. Iv heard the stock carbs on chinese pit bikes are trash so maybe could do with being upgraded. What size carb would be best. I heard you say 24mm in the video. Great video btw and thank you.
Your carb is fine, it just needs to be richer on the 3/4-full throttle. You need to see my jetting videos. This is fixable. Stock Chinese carbs are jetted kinda lean for importation purposes.
i dont really know a lot about this but if you have a big carb, why wouldn't it idle well? at idle, the air goes through the idle circuit instead of the venturi right? so how does it impact the idle?
The venturi does still play a factor as well as the pilot circuit design/size. However its the off idle performance that could suffer if too drastic of a size change is used.
The biggest question here is the manifold port matched to the 50cc ATV head? If so then, yeah you can without too much trouble. The thing is with an oversized intake mated to a smaller carburetor you will loose a bit of intake velocity at the lower RPM and throttle openings. Usually this means the torque curve will be flatter until RPM's build. In extreme cases you can experience pooling of the fuel in the intake and that will cause some sputtering.
Great video! I wondered if you could help.. I'm fitting a Rotax 257 single; 2 Stroke (kart engine) to a bike; any ideas what size Carb i should be looking for for optimum mid/high rev range? i think* stock was a mikuni 38mm carb but not 100%. Any advice would be amazing! Steve
So i have a husqvarna smr 125 which has a 52mm bore and a 29mm carb as stock but that is super small for it (thats what i have heard at least) im think i could get a 32mm carb on it since i have a performance exhaust on it. You think it woulddo me any good?
Is it running poorly now? I mean it depends on where you want the performance to come on. If it is more of a high RPM application then yes the larger 30-32mm would be maybe more appropriate, however if the rest of the internals are stock it may not make much of a difference
@@thejunkman well that carb restricts it a lot because its an A1 bike so it should make 15hp but apparently 32mm makes it full power and im a tad bit confused
Depends if the head will flow that much more. I have a big valve head and high lift cam using a 26mm on my CRF50 with a bbk 140cc. You sacrifice low end grunt for getting out of the whole but the mid is nice and meaty.
Great teaching. I just added a racing cdi and an Pz22 on a 110cc engine that came with a pz19. It cranks and runs fine. I can’t use the choke though. It cranks fine without the choke and when I engage the choke, the engine immediately dies. Problem is the cable is now too short. But I figure I can decrease cable housing to fix that. And It is leaking fuel through the overflow. Should I just go back to 19mm? I’m brand new to this stuff.
You will like a engine with the right carburetor much better than a engine with a large carburetor! It's not going to be that noticable, if you can't enjoy the ride to the high rpm! Basically 2mm larger for more power, 4mm larger if you big bore and cam, port the head, and air filter, and free flowing exhaust, to get more flow for the 4mm larger carb, a 50 cc engine I been working with I went from 39mm bore to 50mm, with a head with larger valves, from 16/18mm, to 18/21mm, with ported head, cam. Exhaust, and from 19mm to 20 mm carb, it still has lots of low end throttle response, but stock type CV carbs are not that available, they come in 18,19, and 20, then 24,28,mm. The 24mm is too much, it idles, but will not rev, it can't pick up enough fuel, too much air, and would be alot of work to get it to run crappy, ( the 24mm is for 125-150 cc in this family of engine) most 150-170 use a 26-28mm, I did find a Yamaha, CV carb that I modified to fit. It is 22mm, it should work, maybe with some further mods, jets and tuning, but I think I'll save it for my 52.4mm bore kit, getting closer to 100cc, being the carb is for a 125cc Yamaha, my engine does spin a bit higher than the stock version peaking at 8500, I have seen 10300 rpm, I try to keep it below 9500-9800, the stock carb didn't want to rev past 9k, great video, it explains things well,
My 125 cc motorcycle now has load, high lift cams, big bore, racing parts, etc.. and currently my carburetor is 24mm, is it okey if i change it to 28mm carburetor? Can get a better performance? How about the jettings?
![BEST GY6 PERFORMANCE MOD! [Plug & Play carburetor]](/img/n.gif)
junkman rules!
You sir have answered a lot of questions I had about upgrading to a bigger carb and informed info's I never knew I needed. Big thanks. Your channel is great.
I went from 24mm to 32mm flat slide with upgraded 7mm lift cam. The engine is 200cc single cylinder pushrod type. It runs good. Though sometimes there's a little bog on mid throttle and sometimes the idle is not stable. I'm thinking that it could be a faulty needle. But its true, at high RPM, it runs like a beast, and its a lot of fun. At low RPM, it pulls like a champ as well. Its just that mid throttle and idle that bothers me sometimes.
It you find that lifting off the throttle makes it try to go, its running weak in that area. or rich if you get nothing from lifting.
Mid range, try lifting the needle by lowering the clip if it has one.
Roundslides seem to be easier to tune same diameter i ran a flatslide 30 on my 150 changed it to a nibbi 30mm ran way better for some reason if u run pwks they dont seem to run how u want them on a 4 stroke
@@Saucethe1 to big carb, try a 26 mm for a 150cc engine
Got a 4 valve zs212cc and I got a 500 dollar proper motorbike carby I wanna use ids 33mm how would I make this work on a 28mm/30mm manifold any help be appreciated thank you ??
@@mikga4528mm for me(150cc)is decent but your right a 26mm pwk for 150cc is best.
I was confused about the decision to buy "Mikuni VM Series Carburetors VM26-8074" or "
Mikuni TM Series Carburetors VM28-418" for my Yamaha Rx100 which has an oversize imported piston, but I'm clear now thanks to Junkman for the crisp and easy explanation, I'm going with 26mm.!
I have a standard 135cc motorcycle using a 25mm carburetor.
I upgraded it to 150cc with some other upgrade such as racing camshaft, high-compression piston, bigger valve, K&N round air filter, leovince exhaust... and I used a 30mm CV carb , it works ok with good performance.
And then I kept the 150cc bore and downgraded to standard camshaft, lower comprestion piston, smaller valve and original exhaust, stock air box filter, but I kept the 30mm CV carb and it didn't work well even though I tried to adjust it. And I replaced the 25mm carburetor and it worked great.
That is some good information. It highlights that internal modifications can have a profound effect on carburetor performance.
Great video!
I have a small 125cc Suzuki (Address 125/FL125/Shogun125, various names in different areas). Since the EFI unit went bad (costs like 300-350 euros to get a new one), I went with the good old way. Converted to carburetor (the Asian version comes with a 18mm Mikuni VM) and used a Keihin PZ 18mm one. Engine had good low-end torque but lacked power on the top-end. Meanwhile, I had literally zero experiance with carburetors. Stupid me, went on to get an OKO PWK26...I tried different jets (32,34,36,37....105,110,115,125...) but still the bike couldn't keep itself idling for more than a minute.
Low-end the engine was like "choking", top end power was good but I felt like it was lacking something. After about 2 weeks of torture with the OKO, I sold it and got a 22mm one. To my surprise the bike runs great! Didn't have to get into jetting, only had to adjust the idle speed a bit. Both low-end and top-end is good and even in cold temperatures, the choke works well so far.
awesome detail! for such a simple thing, carburetors are often viewed as a baffling item.
Yes. And this video is part of a larger series on carburetors in general. I have an entire page on my website dedicated to all information centered around carburetors and tuning.
Holy shit this is a great video. Entertaining, beautifully edited, and informative. Way to step up your game Junkman! 10/10
Thanks. I try to improve something, even if it is small, every time I make a video.
If the carb is a 30mm and the port or opening in the head is 24mm you create a bunch of turbulence in the flow. you might be able to make the bike run but that trubulence can make it hyper-finky to tune and then you have to get into the other things like cams and valve diameters and exhaust and and and.. but the first step should always be matching the carb to the port.
I guess it all comes down to the idle and max rpm’s mandatory cfm “cubic feet per minute “ of air. And the carburetor must be able to perform at both ends of those requirements. The inability to do so will starve the engine for fuel or flood it with too much fuel in the air to fuel mixture.
Pretty much. It seems most people get caught up in the "bigger is better" trap.
I have a 80cc rieju with an 28mm carb and it runs like a monster
@@booz8313 i can respect that. Currently running a 80cc derbi with a 28mm as well. The thing rips so much you can hear it sucking all the air in. It's crazy b
Doesn't work on my 125cc 4 stroke the engine doesn't start with a 28
Glad i found this video I went from a smaller carb like the one in the video and i got a new one same as the bigger one in this video and I cannot get my bike to start now
I've used 26 and 22mm carbs on 212cc and have had good results with both.
That's awesome & interesting
Wouldn't the throttle slide or plate counter act the carb size though? It meters the airflow
You’ve explained it in a way I never would of understood so simple thankyou I don’t know why everyone makes it so difficult 😅
Hi! Can you explain what carburetor size go in fonction with the cc of the engine for best performance ? Thanks nice video !
There’s no solid formula for the ratio of carb size to capacity especially since multiple different engines of the same cc can use vastly different carb sizes
Maybe u gotta try each size, but thats gonna costs a lil bit
In my case im using 30mm carb on my bike, but the performance only good starting middle rpm to high rpm. Low rpm quite poor performance, it feels heavy.
I need to downgrade to 28mm carb to get good at low rpm. Since im using it for daily. Unless im going for touring, then i would use 30mm back.
@@shinjrock7778 what cc do u have and what main jet did u use?
you have to measure the ports and that determines what size carb you get and the most you can get out of it like it determines the biggest one you can get for your bike
I just wanna run this f7. Bad 26mm carb missing everything inside. Now i need to dig around and see what carbs i have around here. I know i have a brand new 24mm mikuni. Its too small but atleast now i know ill have tons of low end power to put-put around in the corn field
on my snorkeled 4wheeler i used pvc no air box just a boot i have a ball valve on the stack to change the air flow if it is all the way open it bogs at wot i close it about 1/4 way to tune top end works for me 30 mm carb 230 cc quadrunner
Thx mate, no wonder my bike sucks at low rpm, the fuel is not atomized properly. U helped me solved months problem😂
I have a klx 143 v1 head it's a trail bike I believe same with the 26mm carb its cold here but I put a bigger jet and dropped the clip to the bottom plug is dark and oily I'm going to get some fatter jets and play around more
If the plug is oily, that is more of a ring or valve guide sealing problem. But you are on the right track with jetting.
I got a 28mm PWK for my 86cc 2 stroke Suzuki K50 moped, peak power between 8-10krpm and runs great, guestimate around 15hp and a bit more to gain with some optimizing work on the channels in the engine block and such.
24mm on my 280cc trials bike, but it can tow a car from idle.
Ordered a 32mm for my Suzuki GP125, aiming for a peak power between 10-12krpm.
How big main yet do you have in pkw 28?
all you have to do is measure the diameter of the port on the head and match that to the closest size carb available anything larger will just hurt performance. for instance the port on my lifan 125cc measured roughly 19mm, so that is the size i went with over the stock carb that measured 16mm, after proper jetting was night and day on the mid to topend. i see so many running anywhere from 22-28mm carbs and unless you port the head on 4stroke or cylinder on a 2stroke to match the larger diameter it does nothing but hurt engine performance and becomes a bear to tune if at all possible.
Thank you for this video I understand it a little more. I have a 150cc scooter that I upgraded to a 211cc. 63mm bore 10.2 stroker. I've notice when I have my 30mm cvk pumper carb great throttle response and top end. So I switch to a 32mm slide and not so great take off its okay but my top end is great. Should I switch to a 30mm slide carb
Depends on your goal. Drivability or top end performance.
Yes I sort of trying to build this for racing with out going to high on the gear ratio for bottom end torque
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I have a brand new 230cc 4stroke dirt bike with a 28mm carb, I cannot seem to eliminate the idle to wide open bog, and it falls on its face type of bog not just a slight hesitation... any ideas? I have tried so many settings and jets with it to no avail?
The problem is the engine design. Those engines have heavy fly wheels and internal parts and just can't react that fast.
I ike doing a smaller D-slide like a PWK and turn off the pumper screw on top
Are 24mn flatslide carb almost equal to 26-28mm round slide carb at full throttle opening? Because of the poor Flow in the round slide carbs at full throttle? Faster airflow/velocity in flatslide and chainsaw carbs then round slide carbs? 🧐
Just a question, how to determine which main jet size is to be used on a certain carburetor? For example, what size of main jet should i use for a 27mm carburetor round slide?
Start with what the manual states for your bike. Then test and try other jets up and down until you get it dialed in. I have other videos on that.
Good morning i rebuilt,a 302,the motor heads,were machine,and i put a 351 cam,do i put a biger carburator,or wat carburator
After ordering a carburetor from China, I am still trying adjustment and it was advertised as ( fits DS80). I have the engine bored and ported. The engine also has a high flow exhaust. It is likely that going back to a stock carburetor is best.
Okay o find this funny I have a 30mm pwk carb on a 50cc! And it runs great it idles better than ever. it rides smooth.
But remember my stock carb was a 17mm carb
He is saying absolutely right i have tried on my 150cc bike with 30mm while its stock is 26mm. Bike pick increase but idling not get tune. Now i am using 26mm pz26 its give good acceleration and idling is also f9. Further i have order some other number pilot jets from which i can get more batter idling.
But plz search any calculation about this thing which make easy to chose carburetor and there jet for best performance at any level?
i have 1997 trx300ex big bore 80mm piston/cylinder camshaft stage 1 rebuilt ..... what size carb should i get oem is 32mm ?
I would keep it as is to start and tune it best you can. If it seems a little anemic in the upper RPM's then I would go to about a 35mm.
I have a 200cc scooter that I changed the carburetor to a 30mm and it'll start,idle,and drive in the low rpms but past about quarter throttle it bogs down and starts popping..... Any suggestions on the jetting or adjustments that I can make to get those about quarter throttle rpms???
Check out mvideo all about it. Or my website. Links in the description.
Is it bad idea to replace CV carburetor to a slide one in a 450cc dual cylinder chopper? what are the cons? hard to find a cv one for reasonable price..
How to tune my 33mm flatside carb it's on a 200cc Chinese motor atv?
Put a traditional 28 or 30 mm round slide carb on that motor. They are notoriously undersized in the port, valve and cam specs
So the 33mm carb is to big for the 200cc engine? If so..Wht size jet I need for the 30mm carburetor?
My dad left me some variaant of a Homelite Super XL from the 1970s. When it runs it has tons of torque and cuts great. But it hasn't run well in years. Probably the biggest issue is the carb. These carbs have a 90 degree inlet fitting that make it very difficult to work on. I've seen tillotson carbs that should fit that don't have that 90 fitting. All I have to do is drill a different hole in the side of the cover and I'm good to go. But which Tillotson carb to choose?
I would find a chainsaw specific forum to answer that question. Too many variables.
Is there a ratio for engine size to carburettor I have a royal Enfield classic 500 which is a long stroke thumper with a 33 mm carb and I have other smaller 200 cc bikes with the same size my plan is to upgrade the 500 to a 42 mm carb with a longer manifold to get better mixing of the gas and adjust the cam timing for rpm will it work or will it stutter midrange I did the same on a custom 200 wher I over bored the engine from 160 cc to 200 it had issues with mixing the fuel past 4000 rmp
It would be nice if it were as simple as Displacement : Carb size, but there are too many factors in that affect what the engine requires as far as carburation is concerned. I may do a future LIVE Q/A and go over this as it is a lengthy explanation that ends with a "it depends". For you it is largely going to be a trial and error process to get a carburetor sizing and jetting dialed in given the modifications you plan to make.
1977 ford 302,rebuilt,machine to biger pistón, machine heads,i had 2 Barcelona carburator, wat carburator can i put to work well
Your camshaft documentation should give you some guidelines on the size. It will also depend on your intake manifold. Something like a 500-650 cfm should be just right.
Helpful endeed....for me being a newbie. i have a 150cc on 28mm, this video confirmed my theory, and shout out to that 125 guy.😁
I have a Chinese cool strip 125CC and it has PZ19 stock carb on it. Is there any point in putting a 24 or 26 mm carb on it then would I have to get an intake Adapter boot? Do I have the wrong thinking about this whole deal?I just want the bike to idle and run better these carbs I keep buying for For 18 to $30 just don't seem to be doing Right and definitely not very long.
Sounds like you need to just fine tune your jetting. The 19mm is just fine
Hi God bless you and your family I have a yamaha yz 85 02 I would like to nkow from you what would be a better carb for my bike than the stock one please let me 3
Know
Keep it stock. That bike will not benefit from fiddling with a different sized carburetor.
If you measure the slide on the left carburetor,you will notice that the slide will be narrower than the opening going to the engine(around to 20mm). This is the reference i take in mind in order to measure, because the air will always have the speed of the narrowest point on the whole intake. Am i wrong here?
Hi Junkman. I have a project bike a 78 dt400. It has a 34mm round slide. I would like to try a 36 mm flat slide carb. I was wondering if for a given size round slide vs. flat side mikuni carb is the float tower talker in the flat slide. I have limited clearance above my stock 34mm round slide as the pipe crosses above it.
Flat slides are usually taller in general, but you could try it.
Hey me I got a 2 stroke blaster I cleaned the original carb still over flowed ajusted the needle still over flowed bought a new stock crab put it on and same thing it over flowed I don’t know what to do at this point and all the shops around me are booth
Did you check the float height?
I have 1 motorcycle 2 stroke at the same time my standard bore stroke are 57mmX54mm.my question,what size bore or piston i need to use carburetor size 58mm for dragrace?
the stock carburetor will be fine, just re-jet as necessary. However if you have a CV type a change to a piston or mechanical slide type would be preferable. See my other videos on that. ua-cam.com/video/i6yOd2lwwDU/v-deo.html&t
My yx 140cc with z40 racing cam rips with a NIBBI 22mm carb
This is the best and true answer!!! Thank you very much Sir!!!
mr. junkman got an 05 yamaha venture took off each side breather and replaced with pods took off all emission stuff runs ok but lost a little snap and alot of top end opened up mixer screw 1/4 turn for more fuel didn't make much difference any suggestions. thank you.
The mixture screw only effects the mixture at idle speed. Try adjusting the jet needle clip position or main jet. I have videos on this
@@thejunkman ok thanks again!!!
I have a problem with this tool, it's a KTM 250 2T
The tool has not been used for almost a year
This week I found time to take care of it, I did a fuel-oil change, I cleaned the filter plug, everything, finally I tried to start it, but the car could not start.
It only started with carburetor spray and shut off straight away
From that I understood that the carburetor needed to be cleaned and that's how I did it.
Now the problem is different, the motorcycle drives straight up to very, very high turns
I played with the air-fuel screw but unfortunately it didn't help.
Is there a situation where the problem is different? Something in the carburetor maybe? need help please
Hi thejunkman. I have a 125cc engine with a 20mm carb. Can I upgrade to a 22mm without doing any internal mods?
You can try, but you will want to port match the intake for sure.
thejunkman. Thanks 👍
I built a 2018 honda 250x 4wheeler for my nephew with a high compression piston, opened up exhaust, opened air box and jetted carb. I was surprised to see it came with only a 20mm carb being a 229cc with around 18hp stock. Would I gain anything from a bigger carb?? I can't find an example anywhere of anyone putting a bigger carb on one of these. Seeing that most 125-140cc engines come with a 20-22mm carb and even the 6hp go karts run that or bigger makes me think that these are undersized and maybe I could gain a lot from a 28mm or so?? Any advice would be appreciated!
Most likely yes
Question. On a 125 honda cm twin with pod filter and slightly modified exhaust, comes from stock with a 26 mm carb. Would you recommend go higher on main jet or go to a pz30 and decrease main jet size? Thanks
If it feels anemic then yes.
just discovered your vids today and immediately had to subscribe. i wish these vids were on youtube when i was learning about carbs few years back in my carb scooter days. you do a great job and insert great illustrations. this particular vid is beyond what i need, i was just curious, but i expected something like: for single cylinder 4t 125cc you use this big carb, for 2t 125cc single you use this, for 4t 250cc single you use this, for 4t 500cc twin you use this, for 4t 883cc twin you use this carb if your cylinders share one carb, but you'd use these two carbs if each cylinder is fed by their own carb... catch my drift? Again, i love your vids and am leaving likes as much as i can.
I or anybody else can't say exactly what carbs one should use for a given engine displacement. Not every 125 4T engine is created equal so what works here won't be the best for over there. Some general rules apply but it relies so heavily on the volumetric efficiency that is built into the design.
May 150cc uses 27mm stock. Planning to upgrade 30mm carb. Is it a good upgrade?
Just saw your vid. My question is the bike I juts got, 2 stoke 250cc (actually like 229c) came with a 38mm carb. Kinda seems too big. The pipe Is a smaller pipe for a 125ccbike. I will be putting on a larger pipe however. So should I stay with the 38mm? It took me a while to get the bike to run without bogging when fast throttling but just not sure if I should go down a size or keep it due to pipe change soon.
2 strokes require a matched pipe for proper operation. Your bike might need crank seals if it is old or worn. Same if this has reed valves or some type of exhaust valve.
Had the same problem on my 70cc bike i went to a 21mm from a 12mm it ran but was so rich it's soaked the matting in my pipe then the bike got to the point where it wouldn't even run I went back to the 12 mm bike runs perfect lots of low-end torque but just like you said I lost top end
You need the smallest possible pilot and main jet to match. The 19mm wasn't in stock when I needed it so I got 21mm too. It is what it is.
You cat put single or individual carburator same size opening in 4 cylinder bike?
Depends. You'll need a manifold to accommodate it.
I just got a new carb for my motorized bike but I couldn't get it tuned right the idol was simply way too high and it wasn't really responding to the throttle. I think the jet size might be too big for the engine?
Greetings junkman. I just bought a 2 stroke motorcycle. The previous owner told me he has change the cylinder bore and piston from 56mm to 57mm. Is it necessary for me to change the 20mm carburetor to larger carburetor seems the displacement has change from 120cc to 125cc.🤔
Thanks.🙏🏾
Generally speaking all the components need to reflect the rpm range that power is desired. Bigger is only better if the power is desired at a higher rpm and cam,exhaust etc need to reflect that. Even then there is a saying in motorpsorts, that horsepower sells engines, but torque wins races.
What is symptom of too big of carburator? Hard starting? I have a tpr 86cc 2 stroke with 30mm flat pwk polini with vforce3 reeda on a yamaha zuma. It is alwyas hard to cold start it. Once it started, starting is no problem,idle is perfect, it rips too on all throttle range..
It is just the starting that i am having trouble with. It basically floods my exhaust maybe around 10kicks with 1/2 throttle before it even start. Choke doesnt do nothing. I have highher chance of starting it with pulled throttle up to 1/2.
Thanks!!
But if I wanted to go one single carb on a 77 CB750 F2/3, I would use a 4-1 manifold witha 34mm Mikuni carb? I know I would have to mess with different jets. Any help?
Is that even a thing? I would not think that would run very well.
Please respond!!! I don't want to blow up my engine again I have a 96 Polaris XLT special with a 580 monoblock comes with 38 mm mikuni's the sled I am currently building had 34 mm mikuni's I took the 38s and put them on the sled I'm riding that had 34s is this going to be okay the other day I blew up the original engine that had the 34s on it had to pull another engine from a different sled out back that had 34s on it that's the one I put the 38s on sorry about the long comment but I don't want to seize another engine this one has awesome compression
There are more factors than carburation at play when an engine seizes. So that might have not been the issue. If you are worried start off with a bit richer fuel mixture, test, then fine tune the jetting leaner doing plug inspections regularly. And if that sled uses oil injection be sure the system is blead properly.
great video!
hope you can help me with this issue.
I have a dual-carb yamaha virago 535 (1994) and I want to convert to single-carb.
Since each of the stock dual carburetors has 34mm, which size should i consider for the single-carburetor conversion? the same size? or do I need to compensate with inside jets? what is your advice?
thanks in advance!
Thank you junkman!
Cool video, so what if you had say a Keihin Pb18 and the Mikuni equivalent.....they would still have slightly different attributes? Like more adjustability of each circuit?
Yes, the design will make a bit of a difference.
question, i know its odd that a certified master mechanic should know this, but i was given a nibbi racing 24mm output dia with a larger 35mm intake dia as my OEM carb.
oem carb is a 33 input, 30 output.
nibbi is a 35 input, 24 output.
id assume that this carb would lack airflow if i were to boot it to my 250cc 4 stroke's intake.
I dont want to lean my engine, I'm okay with a small loss of power, shes an in town putt-round anyway, but more low throttle power is desireable.
ive never asked the question, cam i down size my carb and not suffer too many losses, maybe even experience some gains in fuel economy.
Hey, new subscriber here! I also have a 125cc, changed the block/piston to 56mm now its a 135cc, same deal im using a 28mm carb, regrind cams, intake and exhaust ports are ported and polished(which some people said were too big), big valves, free flow exhaust. with all these mods i only gained little power and it is so hard to tune. So Watching ur video convinced me or made me suspect that my carb is too big for my engine. I also heard that bigger intake ports could lower velocity. Do you think reducing the size of the intake ports could increase power or atleast increase velocity of the air fuel flow? Or should I get bigger cams to compensate with the big carb and ports? What are your suggestions?
It depends on what you want to achieve. Re shaping ports is not an amateur job, especially if you are trying to optimize flow characteristics. I would make sure you have a cam that has enough duration and overlap to keep the air moving and fuel atomized.
i just recently did the same thing got a whole new top end bigger piston to a 56mm which stock is 52 on the 125cc same thing i got valves done 7.0 camshaft and a 28 mm carb should be perfect for the bike try getting more performance stuff to help the tunes more like get a different cdi box different coil for the bike that’s what i did helps with better timing and stuff and get all the power you really want in the bike i had got a 30 mm it works but i feel like going down to a 28 it’s way better and should be perfect
thejunkman Thank you for your suggestion brother, ill try installing a bigger cam. Stay safe and have a great day!
@@thejunkman great video brother, do keep up the good work...I have a quick question for you concerning cvk carb vs the slide type , I have a Honda storm 125 cc and I have noticed that ever since I bought it brand new ,the start up is ok but sluggish when accelerating, I've noticed the same thing with guys who have the same type of bike , after research I've found that the diaphragm type carbs are much slower in reaction to the slide type ...my question is is there anything that can be done to improve the throttle lag and also can I swap out the cvk for a mikuni , if so what size do I purchase and what else do for the mikuni to work? Thanks in advance
@@deniscastro2880 problem here in Philippines their is alot of 2 stoke dirt bikes running around in 125cc and the 28mm works ok with reeds, not so with 4 stokes.
Too big of carburetor on a 2 stroke will reduce peak,it won't reach peak rpm,if you have a 100cc 2 stroke with ported intake and exhaust i recommend putting 24-26 mm carburetor,too big of carburetor will have large fuel droplets meaning it will burn slower,smaller carburetor will have more intake velocity making guving a better atomization and wuicker burn rate
i have a question i have a wave 125 with 57mm block and i want to change to big valve head and im choosing between 28/24mm head or 31/27mm head some mechanics says that 28/24mm head is better to use on 57mm block than 31/27mm head...i dont understand why 28/24 is better than 31/27 head..is the bigger the valve are better right? ineed your help
In some cases bigger valves mean a slower velocity of the air moving in or out. This typically means less low end torque. However, larger valves are better if the engine sees mostly high rpm use. Some where in the middle is the sweet spot. This is probably why the recommendations are for the smaller valve combination. You will need a cam to match this new configuration though.
@@thejunkman how much camshaft lift should i use 6.0 or 6.5 because im planning to have my wave to be drag racing setup should i use large or the right size of valve
my current setup now on my wave 125 is
1.57mm big bore kit
2.6.0 camshaft
3.advance ignition timing
4.high compression
5.24mm flatslide carb
6.stock head 24/21mm
7.racing clutch spring
what other things could you recommend to me to make my wave 125 more powerful
im also planning to get bigger valves and larger carburetor but what size i want to use my wave 125 to be drag racing type btw the stock block of wave 125 is 52mm thanks for replying to my comment😊
What is the stock lift?
i cant find any info about the lift of the cam but aftermarket racing cam you can buy is ranging from 5.3 lift to 7.3 lift maybe the stock cam lift is somewhere between 5.0 to 5.3 idk
Hi Junkman, I have a 77 KE 175 cant find an expansion chamber for that year. Will a 1980 KE chamber work even though its tuned to a reed valve engine?
It will probably work from a design standpoint, however it probably will not bolt up being the mounting points and cylinder port is in a different place so the bends won't make it physically fit.
I threw a 26mm on my powerfist 208cc (go kart,mini bike, woodchipper engine ect) has a 3 stage header, removed governor, fuel pump normal stuff. The stock carb was maybe a or 20mm or so an man its a huge difference lmao
Great video, I have a kz400 with no carb, would it be possible to use a similar sized carb from a Honda, Suzuki or Yamaha, I would have to get it to fit correctly, of course.. thx
What year? To a certain extent yes, but there will be an experimentation period to get the jetting right. The first year used different carbs than later years. I have a 1974 that I restored and then 2 later versions for parts.
@@thejunkman it's a 1976 I believe, once I get out of storage I'm going to try a gs450 carb I picked up for $10, not much to lose for that price, I'll check through your videos, I have much to learn
The carb I have is I think a 27mm, and I found a much better looking 33mm, Thoughts? The engine is a 44ci briggs vtwin, the oem carb has all of one adjustment, Idle speed... The one Im looking at is from an Yamaha Raptor 660.
Probably won't work real well as the intake velocity won't be enough I would guess.
@@thejunkman Well, To even bolt it up to my engine, Id have to make a custom intake manifold.
Right, and that means it might not work the best.
@@thejunkman also by the time I get around to doing the carb swap, it won't have a governor anymore.
Yeah but those engines don't spin much past where the governor is set.
I have full series 100ccm 2t Honda Bali scooter. Im thinking about 28mm carb. Will it be good?
I need your help please. I installed a two mm larger flat slide pwk oko carb on a ktm 50cc, air cooled, case reed w an 80cc exp. chamber. Being 2 mm larger w a graduated (coned) intake, what jet size, pilot should I use? Im pretty certain the stock jet on the stock 19 mm carb(round slide kehein) was a 105-108. werent marked? I compared to dozens under a mag. glass.
You will have to test. Try the stock and see if it runs, then go up from their.
junkman. hope you can enlighten me. a 150cc (62.2mm x48.8mm) DOHC engine, so it certainly lives at the top rpm..peak torque and hp between 8500-9500rpm i think, stock camshaft .. comes with a standard CV carb 26mm.. is 28mm a good upgrade or 30mm? if im opting for 30mm should i change the camshafts at least? what kind of modifications you would suggest for this engine for a higher top end?
What about the venturi size?
I was told that is the real size of the carb.
For an example, pitbike engine 85cc, 70cc cilinder head.
inlet of the Cilinder head is 22mm, and the inlet valve is also 22mm.
So it needs an 22mm, I have a vm22 carb, manifold size is 26,(i made the inlet bigger to 26mm with an Dremel).
Whats your opinion on this?
Well doing what you did will benefit the top end, but sacrifice the lower end torque because the larger opening reduces the velocity of the incoming air.
@@thejunkman so what means the number 22 in vm22?
I used before the vm22 a vm16, manifold inlet size 19mm.
I indeed wanted to improve the top end
22mm venturi size. Now just to be clear, 26mm is a pretty big jump. This engine might just fall on its face at low RPM's and it might be hard to jet for the low/mid range without some issues.
Hello what would be your recomendation on a 150cc with a full system on also Racing CDI, Coils and spark plug and a couple more mods, I’m trying to reach the maximum performance out of it.
I’m looking between a Nibbi PWK26mm or PWK28mm which one should you recommend?
My stock carburetor it’s a Pz27 which measures 27mm on the cylinder side!
Thanks a lot sir I would really really appreciate your thoughts on this matters since I’m new to it
So, if I want to put dual carbs on my I4 honda cb750, how do I pick my carbs, Murray dual carb kit has two vm34, but I don't know how much modification was made to the carb. Any tips?
Does the size of the 2 carbs need to be bigger to compensate somehow?
I have a twin cylinder Honda CD125 Twin Bike with CB points and a 6V system. My engine is running smoothly and with more pulling power at cold weather, Early in the morning and at night. But when I ride during the day when the atmosphere is hotter then the engine is not running smoothly and the engine power is lower with increased engine noise and engine vibration. When I happen to ride from hot atmosphere into cold atmosphere due to raining on the road immediately the engine is begining to run smoothly with less engine noise, with less engine vibration and increased engine power. I wanted the engine always run smoothly as It was in the early days that bought it. On this matter I had many technicians try their skills on my bike and non of them were so far able to solve my problem and bring the engine back to the performance at early days. I am still wondering what could the reason be. Hope to have an efficient answer and advises to regain my engine performances. Thank you in advance....
I have a SSR125 it’s 22mm carb if I order a 24mm same mounting style and all will the bolt holes line up still? Thank you if you see this and reply!
Maybe, but you might have to modify the intake manifold. Ideally you want to port match it.
Hi. I have recently developed a hobby of putting carburetors on non-carbureted engines. Currently I am running a Honda D15B (1493cc 16 valve) with a VW 30/31 (designed for 8 valve 1600cc). It runs great and I am super proud. However, I am flirting with the idea of creating a dual carb manifold. Do you think would be able to run a 2 VW carbs with only some minor adjustments? I feel like it would either *just work* or I would run into a rich condition. I cant find a guide online, do you have any incite? Thanks :)
Is a keihin carb 41mm to much for a cr 250 instead of the 38 that is on?
Depends on if you are going to change the porting or not.
@@thejunkmanyes i'm going toi port it an polish every sharp edge but there are a lot of Fake keihin carbs man!
I have a superstomp 125 (chinese), completely stock. It bogs down in high revs but iv checked the carb and the jets are squeeky clean. Iv heard the stock carbs on chinese pit bikes are trash so maybe could do with being upgraded. What size carb would be best. I heard you say 24mm in the video. Great video btw and thank you.
Your carb is fine, it just needs to be richer on the 3/4-full throttle. You need to see my jetting videos. This is fixable. Stock Chinese carbs are jetted kinda lean for importation purposes.
Thanks man i will give it a watch!
Probably getting too much fuel
i dont really know a lot about this but if you have a big carb, why wouldn't it idle well? at idle, the air goes through the idle circuit instead of the venturi right? so how does it impact the idle?
The venturi does still play a factor as well as the pilot circuit design/size. However its the off idle performance that could suffer if too drastic of a size change is used.
Ok I got to ask what happens if u put a xt500 carburetor on a Honda xl 250 r?
It will probably be hard to tune, but it would probably work.
@@thejunkman oh ok but the xt500 carburetor is already tuned but it will just ideal to high but u get turn the idealing screw down. Right?
You will have to adjust/tune it for the smaller and higher velocity intake of the XL250
Hey I got a question if I have a 22mm intake manifold for a three wheeler I built, can I put a 14 mm on the intake and run it on a 50cc atv engine
The biggest question here is the manifold port matched to the 50cc ATV head? If so then, yeah you can without too much trouble. The thing is with an oversized intake mated to a smaller carburetor you will loose a bit of intake velocity at the lower RPM and throttle openings. Usually this means the torque curve will be flatter until RPM's build. In extreme cases you can experience pooling of the fuel in the intake and that will cause some sputtering.
Ok, thanks for responding to my comment hopefully I can get this thing I’m working on done by tonight
Great video! I wondered if you could help.. I'm fitting a Rotax 257 single; 2 Stroke (kart engine) to a bike; any ideas what size Carb i should be looking for for optimum mid/high rev range? i think* stock was a mikuni 38mm carb but not 100%. Any advice would be amazing! Steve
If you don't care anout idle quality then put a 42mm PWK on it an dial it in.
So i have a husqvarna smr 125 which has a 52mm bore and a 29mm carb as stock but that is super small for it (thats what i have heard at least) im think i could get a 32mm carb on it since i have a performance exhaust on it. You think it woulddo me any good?
Is it running poorly now? I mean it depends on where you want the performance to come on. If it is more of a high RPM application then yes the larger 30-32mm would be maybe more appropriate, however if the rest of the internals are stock it may not make much of a difference
@@thejunkman well that carb restricts it a lot because its an A1 bike so it should make 15hp but apparently 32mm makes it full power and im a tad bit confused
i have a 70cc yamaha fs1. is a mikuni 21mm good for it.
I got a 110 lifan with a stock 20 mm carb what size should I put it?
20mm, that is a good balance.
What about 2 smaller carbies together would that better cover the power curve?
I am not sure what you are asking.
Can I run anything bigger then a 26mm on my 140cc pit bike if so how much bigger.
Depends if the head will flow that much more. I have a big valve head and high lift cam using a 26mm on my CRF50 with a bbk 140cc. You sacrifice low end grunt for getting out of the whole but the mid is nice and meaty.
Great teaching.
I just added a racing cdi and an Pz22 on a 110cc engine that came with a pz19. It cranks and runs fine. I can’t use the choke though. It cranks fine without the choke and when I engage the choke, the engine immediately dies. Problem is the cable is now too short. But I figure I can decrease cable housing to fix that. And It is leaking fuel through the overflow.
Should I just go back to 19mm?
I’m brand new to this stuff.
adjust the float needle
You will like a engine with the right carburetor much better than a engine with a large carburetor! It's not going to be that noticable, if you can't enjoy the ride to the high rpm! Basically 2mm larger for more power, 4mm larger if you big bore and cam, port the head, and air filter, and free flowing exhaust, to get more flow for the 4mm larger carb, a 50 cc engine I been working with I went from 39mm bore to 50mm, with a head with larger valves, from 16/18mm, to 18/21mm, with ported head, cam. Exhaust, and from 19mm to 20 mm carb, it still has lots of low end throttle response, but stock type CV carbs are not that available, they come in 18,19, and 20, then 24,28,mm. The 24mm is too much, it idles, but will not rev, it can't pick up enough fuel, too much air, and would be alot of work to get it to run crappy, ( the 24mm is for 125-150 cc in this family of engine) most 150-170 use a 26-28mm,
I did find a Yamaha, CV carb that I modified to fit. It is 22mm, it should work, maybe with some further mods, jets and tuning, but I think I'll save it for my 52.4mm bore kit, getting closer to 100cc, being the carb is for a 125cc Yamaha, my engine does spin a bit higher than the stock version peaking at 8500, I have seen 10300 rpm, I try to keep it below 9500-9800, the stock carb didn't want to rev past 9k, great video, it explains things well,
I put a 26 mm carburetor on a 125cc lifan engine and did 40 mph also I'm 240 pounds and the engine is on a 50cc taotao frame.
I have A 150Cc China Bike,Will It Run Normally If I Put 125Cc Carburetor? All Can Advise Me,Thanks
No, you will have to re-jet. You may loose some top end power for a gain of lower end torque.
What’s the best carb size for 150cc bike to get more power
My 125 cc motorcycle now has load, high lift cams, big bore, racing parts, etc.. and currently my carburetor is 24mm, is it okey if i change it to 28mm carburetor? Can get a better performance? How about the jettings?
Probably would be beneficial. You will have to experiment with the jetting.
@@thejunkman thank you.. Some 28mm carburetor are 120 main jet and 40 pilot jet.. Is that jettings set are right? Or over jet?
Hey quick question i have 82cc 2 stroke what size carb should i use please help thank u
From 19 to 21mm