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 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.!
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.
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 ??
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.
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 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.
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
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
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
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.
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
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.
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
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.
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 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
The more I think about this question the more I realize a lot of people don't understand volumetric efficiency. A big carburetor works good on a big engine. But what happens when you're at a stop / low idle and you go wot. That 1k cc engine at 500 rpm would eventually be the same as a 500cc engine at 1k rpm. It's not pulling very much air. So if it works good on the big engine at low rpm it should work good on a smaller engine also. It just won't utilize all of the carburetors potential.
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?
I’ve got an aprilia rs125 2005 unrestricted 28mm carb and I was thinking if I put a bigger carb it’ll go even faster, but I also want to wheelie in first😂
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.
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
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?
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?
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,
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? 🧐
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
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?
Ive always found sizing weird. My 150cc scooter engine popularly uses a 28mm carb when built up a bit, and yet built predator 212s use a 24mm at full built capacity
Well it sort of works like this. Smaller bore will maintain velocity which is good for low end torque. On the converse larger bore carburetors favor high rpm power. Intake valve size, duration, lobe separate of the camshaft and cylinder head design and volume all play a part in determining optimal carburetor sizing.
Bigger definitely isn't always better. Gotta find the right balance between air volume and air speed for a given application. Increasing carb size and therefore air volume will decrease air speed or velocity. Being slightly too small will yield better results than being too large. It will pick up sooner off the bottom and be much easier to jet.
I love the t shirt. Thanks for the video. I have a paramotor (basically a chainsaw engine. I realised I had tuned the carb with a spacer missing between the carb and engine. It ran well but when I replaced the spacer (only around 10mm thick effectively pulling the carb further from the engine) it leaned out. Fuel air mix had not changed at all but it leaned out so much it would not run anything other than tick over. Any idea why this would happen ?
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.
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?
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 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!
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..
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 :)
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.🙏🏾
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
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.
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
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
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.
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!
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!!
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
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 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?
All I want to know is can you use a different style carburetor for an engine that it wasn't designed for!? I own an old soviet bike and I can't find a carburetor for it anywhere! So I was thinking of Frankensteining a Honda carb onto it 🙃
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?
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 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
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....
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.
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.
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.
Great video junkman! I have a question for you, hope you get a chance to answer this for me, I'm new to motorcycles but eager to learn! My question is, what size carburator can I upgrade my 200cc 4 stroke motorcycle with? What do you recommend? I want a little more power... Better performance overall... Thanks junkman!
@@thejunkman Hello and thanks for your prompt response, no other modifications have I made aside from the gas filter... (The motorcycle came without a gas filter)
personally i wouldn't worry about carburators as a starter mechanics (if you are one) untill there is a true issue with the fueling. If you want more out of your bike, start with the easier things to do, tires, gearing, weight reduction and better fluids. Engines usually are a last result next to transmissions and clutches because typically there will be the most complicated systems requiring specialized tools and specialized directions. This is not to deter you, but as a heads up for whats to be in store
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 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???
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.
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.
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.
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
![BEST GY6 PERFORMANCE MOD! [Plug & Play carburetor]](http://i.ytimg.com/vi/snhUWQnFgbE/mqdefault.jpg)
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 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.!
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.
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.
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.
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 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.
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.
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 😅
I've used 26 and 22mm carbs on 212cc and have had good results with both.
That's awesome & interesting
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
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
Thx mate, no wonder my bike sucks at low rpm, the fuel is not atomized properly. U helped me solved months problem😂
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
Wouldn't the throttle slide or plate counter act the carb size though? It meters the airflow
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.
This is the best and true answer!!! Thank you very much Sir!!!
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
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.
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
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.
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 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.
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.😁
The more I think about this question the more I realize a lot of people don't understand volumetric efficiency. A big carburetor works good on a big engine. But what happens when you're at a stop / low idle and you go wot. That 1k cc engine at 500 rpm would eventually be the same as a 500cc engine at 1k rpm. It's not pulling very much air. So if it works good on the big engine at low rpm it should work good on a smaller engine also. It just won't utilize all of the carburetors potential.
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’ve got an aprilia rs125 2005 unrestricted 28mm carb and I was thinking if I put a bigger carb it’ll go even faster, but I also want to wheelie in first😂
We should remember if stock is 16mm diameter, and if you put 19mm diameter carb on, it is 40% biger flow!
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.
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.
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.
thanks bro,now i know whats wrong with my bike,its over size,
Thank you junkman!
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 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.
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,
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? 🧐
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
My yx 140cc with z40 racing cam rips with a NIBBI 22mm carb
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?
I have a 30mm flat side carburetor on my 50cc moped
Ive always found sizing weird. My 150cc scooter engine popularly uses a 28mm carb when built up a bit, and yet built predator 212s use a 24mm at full built capacity
Well it sort of works like this. Smaller bore will maintain velocity which is good for low end torque. On the converse larger bore carburetors favor high rpm power. Intake valve size, duration, lobe separate of the camshaft and cylinder head design and volume all play a part in determining optimal carburetor sizing.
@@thejunkman huh.....interesting! I cant wait to see how it wakes up swapping from the 24mm cv to that 28mm slide with a cam and intake 🙏
Bigger definitely isn't always better. Gotta find the right balance between air volume and air speed for a given application. Increasing carb size and therefore air volume will decrease air speed or velocity. Being slightly too small will yield better results than being too large. It will pick up sooner off the bottom and be much easier to jet.
May 150cc uses 27mm stock. Planning to upgrade 30mm carb. Is it a good upgrade?
I love the t shirt. Thanks for the video. I have a paramotor (basically a chainsaw engine. I realised I had tuned the carb with a spacer missing between the carb and engine. It ran well but when I replaced the spacer (only around 10mm thick effectively pulling the carb further from the engine) it leaned out. Fuel air mix had not changed at all but it leaned out so much it would not run anything other than tick over. Any idea why this would happen ?
The cut away to this mad lad with a chainsaw❤😂
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.
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.
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.
I have a 27mm carburetor on my 70cc 4 stroke engine
How does it run full throttle and no throttle?
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
I got a 229cc with a 28mm carb
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..
Is it bad to keep it like that
Thanks, Mate great video easy explanations...
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 :)
Love the shirt man
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.🙏🏾
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
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.
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.
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
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
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 👍
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!
What a fantastic and educational video! Thanks!
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!!
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
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
}
amazing video made me want to follow
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?
thank you!!
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?
All I want to know is can you use a different style carburetor for an engine that it wasn't designed for!?
I own an old soviet bike and I can't find a carburetor for it anywhere!
So I was thinking of Frankensteining a Honda carb onto it 🙃
You can, with some time devoted to jetting it properly.
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?
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.
Can you get a Waterproof pod filter
This one was ... good !!!! congrats ...
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
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....
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.
Junkman can you put any carburetor on a 49cc
No, it will have to fit the flange at least. You can probably put a mm or 2 larger and some re-tuning for the increased air volume though.
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.
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.
What about jettings?
I have a dedicated video for that.
Great video junkman!
I have a question for you, hope you get a chance to answer this for me, I'm new to motorcycles but eager to learn! My question is, what size carburator can I upgrade my 200cc 4 stroke motorcycle with?
What do you recommend?
I want a little more power... Better performance overall...
Thanks junkman!
What other modifications have you done?
@@thejunkman Hello and thanks for your prompt response, no other modifications have I made aside from the gas filter... (The motorcycle came without a gas filter)
personally i wouldn't worry about carburators as a starter mechanics (if you are one) untill there is a true issue with the fueling. If you want more out of your bike, start with the easier things to do, tires, gearing, weight reduction and better fluids. Engines usually are a last result next to transmissions and clutches because typically there will be the most complicated systems requiring specialized tools and specialized directions. This is not to deter you, but as a heads up for whats to be in store
What’s the best carb size for 150cc bike to get more power
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 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.
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
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 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.
What maximum size carburetors can be use for a 200cc motorcycle?
It depends on the engine type and configuration. 38mm is getting to the limit.
I have full series 100ccm 2t Honda Bali scooter. Im thinking about 28mm carb. Will it be good?
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.
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 a 70cc yamaha fs1. is a mikuni 21mm good for it.