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.

Holy shit this is a great video. Entertaining, beautifully edited, and informative. Way to step up your game Junkman! 10/10

awesome detail! for such a simple thing, carburetors are often viewed as a baffling item.

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.

What a fantastic and educational video! Thanks!

Thank you junkman!

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 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.!

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 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.

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 😅

This is the best and true answer!!! Thank you very much Sir!!!

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.

Thanks, Mate great video easy explanations...

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.

Thx mate, no wonder my bike sucks at low rpm, the fuel is not atomized properly. U helped me solved months problem😂

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 ?

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?

This one was ... good !!!! congrats ...

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!

I've used 26 and 22mm carbs on 212cc and have had good results with both.

super helpful ! Cheers !!

Thanks a million if it's nit to much to ask bg or small how do fit the engine side opening where the air filter side will need a smaller or bigger tube thanks

Good stuff... thanks alot

Very informative 👌

What is your advisable for my 125cc china bike .I'm using 26mm nibbie super sport.my problem is it's good on idle and 1/4 throttle but when I rev up my engine slows down

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

So much help! Thx u

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.

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.

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?

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.

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 full series 100ccm 2t Honda Bali scooter. Im thinking about 28mm carb. Will it be good?

thank you!!

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?

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.

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

Is UMA RACING 28mm carb good for a SUZUKI EN125-2A(125CC ENGINE) upgraded with SUZUKI DR150 cylinder kit?

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.🙏🏾

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 :)

amazing video made me want to follow

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 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?

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?

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?

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 being so informative!

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

Awsome video

Wouldn't the throttle slide or plate counter act the carb size though? It meters the airflow

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....

May 150cc uses 27mm stock. Planning to upgrade 30mm carb. Is it a good upgrade?

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

What’s the best carb size for 150cc bike to get more power

i have a 70cc yamaha fs1. is a mikuni 21mm good for it.

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..

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

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?

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

Hi! Can you explain what carburetor size go in fonction with the cc of the engine for best performance ? Thanks nice video !

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? 🧐

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

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.

Hello sir for 80cc can I put 28 carb? No has 26

Hey can i put a 200cg carburetor on my 150cg motorcycle

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.

Love the shirt man

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’s the best carburetor for a 250 4stroke

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

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.

My yx 140cc with z40 racing cam rips with a NIBBI 22mm carb

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 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?

Is it bad to keep it like that

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 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?

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.

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!

I have a 30mm flat side carburetor on my 50cc moped

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?

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?

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.

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 have 1997 trx300ex big bore 80mm piston/cylinder camshaft stage 1 rebuilt ..... what size carb should i get oem is 32mm ?

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 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!

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.

Hey quick question i have 82cc 2 stroke what size carb should i use please help thank u

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.

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

Can you get a Waterproof pod filter

Can port and polish making the engine higher compression make you able to upgrade and equip a higher size of carb?

1977 ford 302,rebuilt,machine to biger pistón, machine heads,i had 2 Barcelona carburator, wat carburator can i put to work well

My bike runs lean/ needs choke in low gears. Would it be a good move to upgrade?

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 🙃

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

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!