50cc Carburetor tuning for Keihin CVK on a QMB139 Chinese scooter engine

Main jet kit: www.partsforscooters.com/114-4...
Air filter: amzn.to/2ref3uw
Carburetor: amzn.to/2JL7li2
0:00 intro
0:57 Main jet
3:37 Elevation
7:26 Pilot jet
10:00 Idle
11:47 Needle
13:11 Accelerator pump
13:36 Temperature
14:21 Summary
This is a complete tutorial showing you how to tune a 50cc Chinese scooter carburetor. I will show you how to select the right jets, check the spark plug, and how to tell if the engine is running too lean or too rich.

[@sarahthibodeau6439]

This guys a real rocket scientist this is the best most complete carb tuning Video I’ve ever seen A+

[@rannolong5435]

Can someone describe to me what the sharp odor smells like? Cuz I have a harsh burning rubber smell and I can't find out why

[@bobcranberries5853]

Sbeary was going to say the same thing. I’ve seen lots of videos on carb tuning but this one is by far the best.

[@alberttonson3191]

@@rannolong5435 a slippery clutch maybe, if your clutch is slipping its going to burn off the clutch material therefore it smells

[@Orlena2525]

Did he mention float adjustment? I don't remember him mentioning that. But everything else was awesome!

[@michaelbearse4733]

Yea it is.

[@driffbro3380]

I now am a PhD in carburetor tunning thanks to you👍

[@thelagmeister]

Holy crap is that road rash? I just went back in time.

[@gfsfgffdd8984]

ن٠

[@tmhchacham]

Wow! _Excellent_ video. It all makes sense now. Though, i will have to watch the video a few times to absorb it all. Every video should be like this. Explanation, step by step, case analysis, recap. Thank you for being amazing.

[@michaelbearse4733]

Me to mydude. Theres allot of in for in this video

[@RellyOhBoy]

This is one of the best "carb tuning for dummies" videos l've seen so far. I would assume this would also apply to 150cc engines as well (except the jet sizes will be larger).

[@Mikeb8134]

the carb is probably the same as the 50cc.

[@ambushb0y]

The amount of in depth detailed information quickly makes this video everything I wanted to know, thank you

[@leath25]

At last someone who actually knows what he's talking about.carl from uk.

[@LabCoatPaul]

Thanks for the compliment! A video is a tool. It must be efficient and easy to use. I’m happy it helped you.

[@jaymcbride4081]

Paul Shpakov I need your help with my gy6 150cc scooter please.

[@LabCoatPaul]

@@jaymcbride4081 The tuning procedure on the 150 is almost the same as this video. I do have a 150cc tuning video as well, but it's not as good as this one.

[@andrewf8486]

14.7 is the ideal stoichiometric ratio, but it isn’t the ratio that makes the most power. Depending on the engine that ratio is in the range of 12.5 to 13.5. This is because under load and at high rpm the molecules of air may not be close enough to a molecule of fuel to burn. The increase in fuel increases the probability of fuel being in the right place at the right time for the flame front to propagate.

[@LabCoatPaul]

@@andrewf8486 Yes, a bit on the rich side makes more power. By trying different main jets to find the fastest one, I probably end up somewhere around that ratio.

[@MarcusTwyford]

Wow, impressively thorough and detailed explanation of how a carb works, AND careful, methodical explanation of how to tune and diagnose for a variety of conditions. You sir, did a great job!! Wish all KZbin videos were half as informative and helpful. Thank you!

[@4Borings]

Excellent Job Paul! I've watched a bunch of carb adjustment videos and I believe yours is the best.

[@arunmoolan1]

Wow.. Thank you so much for your expansion, with simple and perfect animations. This is what we call art of explaining stuff.

[@richardbarlow7520]

the very best video I have seen on tuning carbs for these little scooters. Thank you so much for taking the time to make it. Now I have to watch it again because there is so much information in it.

[@gmcjetpilot]

One of the best explanation of jetting a small scooter motorbike Carb... Your explanation and graphics confirmed and reinforced my understanding and tuning techniques. .

[@mikeh3334]

The hands down best gy6/qmb scoot carb tuning video. You have helped a lot of folks. Thanks brother.

[@Brian_IA]

I appreciate all the work you put into this video. I'm a novice trying to get a scooter running for my college-bound daughter. Thank you for explaining it so well!

[@baccusthedrunken]

awesome explanations and editing !

[@jamiemcclyment775]

Ive seen so many videos on carb tuning and this is the best one I've seen hands down. Thanks so much breaking down every step you did on order to understand the cause and effects. Great job and I look forward to more from you!

[@LabCoatPaul]

Thanks for watching! Check out my Chinese scooter playlist: kzbin.info/aero/PL1_JDBt1LSiJQETjZiOFXBKtv-ZzfqEx0

[@D3kerala]

​@@LabCoatPaulhi

[@davidcarr1391]

Excellent tutorial.... very clear and informative. I have watched several other videos explaining separate parts of the whole 'tuning puzzle' but this is the first complete and concise version I have found. Thank you for sharing...... it has helped me alot!

[@kachiskid]

Paul, what the heck are doing out there....besides KILLING IT! This video is the clearest most helpful video in our little scooter community! Thanks bro, I will make this my guideline in tuning my carb. this spring. All the info anyone will ever need! Hats off!

[@LabCoatPaul]

Thanks for the awesome compliment and good luck with your scooter! Keep in mind, tuning a carburetor requires a bit of patience. You'll probably have the carburetor out of the scooter 10 times like I did, before you find exactly the right settings.

[@osmiumsoul9535]

One of the most useful carb videos without the filler. Super helpful

[@MasterMine85]

I found this is the coolest video explanation for tuning carburetor! Great editing too! Thank you very much!! From Malaysia 🇲🇾😁

[@williamirizarry1113]

This is really informative. Impressed on how much information you got in in 15 minutes!

[@therealmyhandy]

This has honestly been the best video I've ever seen on carburetor adjustment. all about the practical application, doesn't overload me with scientific mumbojumbo that I'll never use, and really makes understanding the concepts and applications of carburetor adjustment palatable for the common wrencher.

[@LabCoatPaul]

Thanks for watching! That is exactly what I was going for. :)

[@ashwinprakas606]

Awesome video, I show this to my friends every time they think about going free flow on the intake. Too much trouble for so very little gains. Keep up the good work.

[@miguelpedraza5064]

One of best videos for carb tuning out there on ANY PLATFORM!!!

[@johngooch847]

Finally! I’ve been trying to find a video like this that explains each jet in detail. Nice job!!!!

[@joshuabuck7293]

This is by far the best tuning video ive came across, thank you!!

[@benficacm]

This is hands down the best carburetor jet tuning tutorial out there. Thank you, Sir! I would like to add that if your needle isn't adjustable like the one in this video, you could put small washers on it to raise it and at least test it on the rich side. Great video.

[@LabCoatPaul]

Thank you! yes, adding washers to the needle would make the mixture slightly more rich at mid - throttle.

[@dekoldrick]

This is the best tutorial I've found so far. Been google searching how to tune for the 80cc big bore kit I installed and every google search is like people trying to protect some kind of international secret.

[@LabCoatPaul]

I've seen that too. It was hard to find some of the information for this video.

[@joebrennan4249]

Absolutely the best carb tuning tutorial ever. Well done, well explained and I can appreciate the effort you put into this tutorial and the work to ensure your scooter is running the best it can. From the graphics, animations , on board video, tripod shots sped up of removal/install clearly showing the parts etc. It’s super helpful and helps me better understand each function and how to troubleshoot carb issues and how they relate to specific engine running conditions. The only thumbs down I have is Pawshina looks to have outgrown her scooter...but yet still having a really good time!

[@joseluisgutierrez8254]

I have a custom 1980 xs650, after doing tones of research I could not get it to stop running rich I was so confused, after watching this video, I fixed my bikes issues and she's running like a dream, thanks a million professor lab coat guy!!!

[@FrankExelmans]

Finally a complete review from carb working till adjusting ; great video

[@rashadhasan677]

this is by far the best video on carb tuning I have ever seen straight to the point great videos and a recap BRAVO !!!! im going to subscribe

[@ivancudina93]

The best carb tutorial for scooters on youtube. Comparing this tutorial to others is like comparing Heisenberg with Jesse Pinkman.

[@alwilliams7889]

ive watched many carb videos. this sums up everything in a professional and informative way good job

[@dehCremus]

Dude, I've watched a lot of carburetor tuning videos to tune my DR500, but this was definitely the best! Thanks a lot man, now I completely know how my carburetor works and why it's running bad.

[@EzMeck]

What an outstanding video this is! Loved every second of it, thanks!

[@ShahabLodhi]

The bessssst video on tuning carbs i ever saw, thnx man from Pakistan

[@patrickgonzales8072]

Good Job, great video! Adjusted the needle hight on my zuma 50 and now no hesitation mid range.

[@jaywilbur515]

That was about the Best explanation with awesome diagrams on how CV carbs work whether big or small!! How about one on a 4x CV carb setup :) :) Two BIG thumbs up man!!

[@miketabler5588]

Dude, you ROCK! BEST INFO on the net by far what it comes to tuning your 49cc carb. Huge help, thx!

[@GarikKazarian]

i like the doctors coat , nice touch!

[@edboer2851]

Garik Kazarian haha docter throttle

[@rickellithorpe7428]

Best video I have see on scooter carbs.

[@neotheseattledj]

I have watched this easily 10 times while setting up the the new carb for my scooter. everything is laid out so easy oto understand.

[@LabCoatPaul]

I'm glad it worked for you, and thanks for the views! :)

[@kristofferrydquist8384]

You sir, are a brilliant teacher. This is crisp, fast, easy to understand and I am grateful and confident I’ll soon have my scooter running perfect. Thank you!!!

[@LabCoatPaul]

Thanks! I try to provide the information you need and not waste any time.

[@kristofferrydquist8384]

Update: After applying the method described, plus a valve adjustment, my scooter starts immediately, idles perfect both cold and hot, does not smell and pulls strongly on all speeds.

[@TrailRecordingsINC]

best and most informative carb tuning guide THANKS FOR THIS

[@hornetscales8274]

I always had a rule about carburetors: Don't Touch!!!! Since mine decided to get clogged and had a few things go screwy on it, I had to break the rule. Glad to have found this video. REALLY needed the info. Thanks.

[@gocaveman]

Excellent explanations

[@michaellehto1697]

14,7 gives you lambda 1, but a ratio of 12 to 1 gives you most power. Great vid!

[@LabCoatPaul]

If you want to get technical, yes, slightly rich will give you more power. Thank you for watching!

[@nadzrielmaddas8639]

Great explanation, the most detailed carburator adjustment ive ever watch

[@GerinHarada]

My scooter was bogging down alot after his vid i adjusted the vacuum needle and it works fine. Your the man excellent help from you Thankyou so much 👍🏻👍🏻

[@Firdausexehastoppedworking]

This is one amazing carburetor tuning class that youtube recommends me. You got a sub for this

[@Prittyboy203Gaming]

Man this is the best information filled video I have seen you make it very easy to understand and has a lot of writing to go back and pics to double check while fixing my bike awesome and actually works 👍

[@LabCoatPaul]

Thanks! I'm glad it was helpful.

[@MannequinSmiles]

this is the only video where i have actually learned something about my engine. props

[@yellabr10]

Excellent video I slowed the play speed down so I could absorb all your information thanks Doc.

[@michaellodes5382]

This is the video every scooter dude should be watching!

[@bobcranberries5853]

I’ve seen lots of videos on carb tuning but this one is by far the best. If someone finds this hard to understand they need to watch it about five times.

[@LabCoatPaul]

Thanks! I'm happy to help.

[@thomasdsmith7678]

Back in the day, on a dyno, we used to put tape on the throttle grip and mark closed, 1/4, 1/2, and full throttle to make it easier to re-jet and compare power output.

[@kermitdekikker2308]

This is the exact explanation I was looking for for so long, thank you!

[@odysseus2843]

The most elaborate I´ve ever seen. Thank You!

[@atemplin843]

Hands down, absolutely best gy6 carburetor video I've seen yet!

[@LabCoatPaul]

Thanks! I'm glad you like it. :)

[@RadarOfFdd]

This is gonna help me so much with my scooter`s problems! You`re a lifesaver :)

[@overrevtrev]

The mad scientist appearance is hilarious, very simplified helpful video thanks for the help keep up the good work!!

[@vojtechpilar5809]

OMG! This is the absolute best explanation of how a 50cc carburetor works! It finally makes sense!!!

[@LabCoatPaul]

I'm glad you liked it. Thanks for the compliment, and good luck with your scooter! :)

[@sus8e462]

Best presentation and explanation of the options and interactions I've seen! And I've been watching a lot of vids now as trying to get my scooter running again! And last few times I rode it--after a "professional" tune up--it ran shitty. Until seeing this video, I was just worried about cleaning the carb & making sure the jets weren't blocked! Checked my jet sizes (35/88), so all makes sense it was running too rich! (It had ran well for the first few years I got it from the dealer, so really suspect the intelligence of the guys who last worked on it) So glad I'm finally teaching myself how to take care of it and a video like yours satisfies my engineering background and the hands-on/work bench sides of me!

[@LabCoatPaul]

Thanks! You can definitely tune your scooter better than the shop. I've had many bad experiences with scooter and motorcycle shops too. Now that you've watched this video, you know more about carburetors than those guys do.

[@altezzax7]

This is SUPER A++++ explanation on carb tuning! Thank you!

[@jasond.valentine5931]

this was an extremely well explained and executed video. Very informative and i can't thank you enough kind sir.

[@davewebber9246]

Best carby explained so far. Well done

[@bradeleyfan]

Thank you very much❤ This video is really detailed for me to replace one new Keihin CVK Chinese 50cc scooter engine. You are really amazing to be a nice teacher for scooter carburetor at this clips. Thanks again🫡

[@riadhch5643]

THANK YOU PROFESSOR IT WAS THE BEST CARBURETOR TUNING EXPLANATION VIDEO EVER

[@brij4174]

Great vid. I recommend watching at 75% speed though. Dude talks fast.

[@slugg6632]

Already ahead of you 😂😂

[@Goc67]

Well explained and graphically presented again. Thank you.

[@anonymousmysterious4095]

This is the best video on the internet about tunning 50cc scooter! And I'm not even joking! PS. you solved a lot of my problems that I have with my scooter.

[@LabCoatPaul]

Thank you! I'm glad it was useful. I have several other scooter videos on my channel. My goal is to have repair videos for everything a scooter might need.

[@kevinstearns4198]

@@LabCoatPaul my 150 scoot is going thru gas like crazy could carb be no good? it runs awesome but then again...

[@LabCoatPaul]

@@kevinstearns4198 Can you smell gas at all? Maybe you have a leak. Or you could try a smaller main jet. Smaller jet means it will use less gas. Take it on a long stretch of road where you can hit your top speed. If the smaller jet hits the same speed, you can probably use the smaller jet.

[@kevinstearns4198]

@@LabCoatPaul no gas is leaking the plug is the right color i think its the carb. the top end is weak that could be a reason.

[@techn1kal1ty]

Salt Lake! A local like me! Thanks for the awesome video about how to tune these awesome little bikes way up here :) Thanks for the expertise.

[@derekenlow7607]

This is what I expected to learn in school thank you

[@DONphantasmo]

Wow, that was actually one of the best tuning videos I've seen. Great job!!!

[@CulichorHimself]

Man, what a WONDERFUL video, Thank you SOOOO MUCH!

[@flipykicker]

Well done man , beautifully explained video and probably the most conveying also.ty

[@jhonatancrivocapich5605]

My god man, you should charge for videos like this, great job.

[@pedrotalavera3541]

Excellent video with lots of info. Thanks Paul.

[@takatumba]

the best video I have seen in my entire life!

[@danel557]

best video , and trust me that i'm looking for a video like this for quite a while , 10+ for video and explaining

[@dosplatosfoo]

Best Carb explanation Ive ever seen, thanks'

[@mikeadair4471]

Best carburetor video! Thank you so much for this!

[@itsRightThereMan]

Amazing video, thanks Paul.

[@NiftyAutomotiveKnowHow]

Bro, you definitely got it going on. I have a first gen Chuckus with a 80cc bore kit on it that hates me for some odd reason. Tomorrow I'm going to pop this carb off and check, but I guarantee I'm sitting at a 75 jet. I'll update this tomorrow.

[@nickkaarslev290]

You really have alot of effects from different jets, i ride with the same jet year round, now with a foam filter but its the same jet as when i had the stock filter, and it rides perfectly, also got a performance exhaust on it now, and thinking about increasing the jet size from 86 to 88 or 90, will see.

[@mick2d2]

Life saving video! 8) Best explanation I've seen so far, thanks!

[@ktmdukelife9173]

Thanks man, best vidio i have seen about this topic

[@charredskeleton]

Nice video, well put together. Good info. Excellent focus.

[@roserecruitments6762]

Better practical explanation than my college sir. Thanks a lot.

[@PadmaDorjee]

This was so comprehensive, thank you.

[@kirkgigliotti7062]

all how to videos need this information setup and organization! perfect! :-)

[@MiguelGarcia-zy7lu]

This video is sooo useful thank you for saving my time

[@timr617]

Thank you so much for this incredibly useful video tutorial. You helped me fix my problem 👌👍 Subscribed

[@LabCoatPaul]

Thanks for watching! I’m glad it helped you.

[@doug0823]

great video. explains a lot of what issues i am having with my taotao 50. Also explains what a PIA the taotao 50 is and how much work it always takes to keep it running. no wonder they are so cheap.

[@pinoyexplorer8812]

At last I found the right person in YT👌👌👌👌. Thank you 🙏

[@daikimyramirez766]

by far the best carburator tunning video ever

[@LabCoatPaul]

Thanks! I plan on making the same video for 150cc soon.

[@TT.Hell.]

This is well spent 15 minutes, very well explained. I have some problems with my scooter, working my way up in main jet right now. It runs decent but I dont think it gets enough fuel on full speed. It also stalls at idle if I do a quick twist and release on the throttle. Btw, I had the same ways with tha air filter box, removed and it wanted bigger jet. But I hate the noise from the open filter so I think I will modify a stock air box to work well. Maybe an open filter inside the box and more holes to get it flow enough. My scooter is 72cc and does about 70 kmh/44mph. I just want it strong, it does not need to go faster.

[@joku8900]

Man, this video was golden. After watching this video and doing diagnostic & mixture adjust I managed to get my scooter run at idle. Idlespeed screw was cranked too much and it skipped whole idlesystem. Symptoms was that scooter did idle like 10sec and then shutted down. Used your basic setting which you told in this video; 2 full turns idlespeed screw when contacting throttle lever and mixture screw full closed and unscrew it full 1 turn. And boom; holy shit, idle was there

[@morkovetz]

Very good information. Thanks!

[@dw4940]

EXCELLENT tuning video!

[@johnclark7957]

Great detailed video. It has to be rewound. or played at three quarter speed, to pick up the information.