Pilot Air/Fuel Screw Adjustment Explained - Single Carb - Part 1 

Damn haha, thanks for the video. i just found out that i've been adjusting my air screw instead of what i thougt was a fuel screw. I was getting really confused with the reversed outcome of turning it in and out and choking out the bike. You learn something every day.

GREAT tutorial!! Your definitions and examples were perfect. Thanks for your effort!

If you rev engine it should return to idle RPM easily. If they dip below idle, try leaning the pilot screw. If they hang and take a while to return, try enriching the pilot screw.

thank you bro! i was searching for an English channel! because i cant understand hindi!

Wow excellent vid. Dad just bought the Boyz there first atv’s. 70cc witch is really tiny and cold blooded and a 125cc for my 7yr old. 70 hard start. 125 no problem. Half turn thanks to u and is so easy to start it’s almost the same as the bigger 125. U Da MAN!!!!!

This is exactly what I needed in good layman language! Thank you.

Your video saved me soo much trouble and concern by narrowing down the problem with my bike, Thanks! (specially the part you explain if screw is by the motor its fuel - not air)

Now this man knows what he is talking about!!! Many you tubers have no clue !

Keep up the good work brother! Great video!

Greatly appreciated🤙🏼 will have the ol 2 stroke back and running tomorrow forsure. Kept fouling plugs. Running too rich. Definitely needed this video

I typically adjust each carb 1/2 turn at a time. I try to reach peak & smooth idle RPM as a starting point. Sometimes, if any hesitation or bogging occurs upon acceleration, the idle mix may have to be richened slightly.

That was super helpful, thank you so much. This helped clear up my service manual’s instructions as well.

Very helpful to get my CRF150 running to sell, much appreciated! Now I won't feel like an ass selling a sub-par running bike!

Great video sir. You very good at explaining things....a natural teacher.

"You're screwed" Haha I see what you did there

Subscribing and 100 more if I could!. Just bought a bike pretty much starting new on motorcycle stuff and riding ....you sr are a great help! Thank you so much

You have answered SO MANY of my questions in the first minute... Thank you for making it easy to remember and understand!

Thanks for this. Been wrestling with an issue with my Honda GX620 engine for years. Finally found/realized there is a pilot air screw on the inlet side. Knowing that this is what it is, and screwing in richens up the mixture is the key. It ran better when I did this, but I wanted to be sure, as it seemed counter intuitive that in is richer. Now knowing that what I was doing makes sense, I can tweak it a bit more, plus feel confident that I might finally have this solved. Many thanks again for a clear, concise, and no BS video.

Amazing video and excellent demonstration. Not overly detailed but just enough to understand. Thanks for making this video.

The air screw you replaced meters air to the pilot circuit. The pilot jet supplies fuel to pilot circuit and is located in the float bowl. I would check for vacuum leaks. It's easy and I have a vid on that. Next, I would pull the carb and verify pilot jet, main jet, needle, & needle clip position and compare to stock. You'll probably find a leaner pilot jet in there. Also, a leaner needle clip position can to some extent provide a bog like you have.

Great video. I have a rough understanding of carbs, and this video helped me to figure out exactly what each screw does Now my little 110 ATC is swamping like never before.

OK. Water is a byproduct of combustion, and it condenses on the cold exhaust pipe, eventually leaking through the hole you mentioned. I wouldn't worry about it. Although, I would ride the bike long enough to get exhaust HOT to burn it all off.

Excellent explanation for a mechanical dummy like me. Thanks

Top video mate

Thanks for the easy to understand directions for tuning a carb. I grew up on carbs, but never knew enough about them to fine tune them. It was factory or get someone else LOL

the exhaust, I noticed I had oil seeping through cylinder head gasket so I removed cylinder head replaced gasket then noticed the feeler gauge and realized that the .008 refers to inches not mm. Turns out this gauge at its lowest is .20 manual calls for intake btwn. .05-.10 And exhaust valve .12-.17 I have adjusted valves to proper clearance and will start her up. This might be the solution? IDK but it is a problem if not set right thanks again will keep you updated I am grateful you responded. ... This is my first rebuild

Matthew MC Repair-he doesn't even know does he What a refreshing oasis this video is. Mat probably thinks people that don't know what they're talking about would never waste their time making videos. YOU WOULD BE VERY WRONG MAT Most of the Honda XR 250 videos posted, I swear to God I don't know how these people find the door to get out of the house in the morning. Most of these videos are posted by people who bought an old dirt bike, put gas in it, kicked it and it started. THIS, THEY ARE CERTAIN MAKES THEM A CERTIFIED MASTER MOTORCYCLE MECHANIC. THANK YOU AGAIN MAT.

Awsome video! Really helpful thanks man!

That line running to boot #2 is a vacuum line to actuate and allow fuel to flow from petcock.

It wants more fuel. Increase pilot jet by 1-2 sizes. Also check for vacuum leaks.

Best tutorial on YT

Well thank you for this video.

You need a longer screwdriver.lol.

It helps a lot for me that is new in motorcycle configuration. Thanks man! :)

Great explanation! I'm saving this to my favorites.

If it runs better with choke on and takes a while to warm up before turning choke off, chances are the carbs maybe dirty and/or lean jetting.

I searched so long for this information. No one i ever asked could tell me how to know if its adjusted correctly (besides checking the spark plugs which still doesnt tell me what to do) This is a perfect tutorial. Short and full of information. Thanks

I've got a Honda shadow 125, recently put a silver tail exhaust on. If I had to, would I be able to get away with just adjusting the screw rather than new jets?

Very informative.

400ex? When you slowly apply throttle or when you stab it?

Your video really helped me out out man, thank you!

Now that was a great video bud 😊 , great stuff

Damn! This was the cat's meow! Perfect video making perfect sense...thank you so much for your help! My carb Suzuki DR200 has the idle screw on the bottom of the carb...what a pain in the tush to get at it! Mine seemed to be happy at about 2-1/2 turns...

Great sound when your reving it

Great video! Quick question. I cleaned and rebuilt the carbs on my Virago 1100. I synched them last night and the bike seems to be running well. However, when I went to adjust the pilot screws, tightening the screw (on the front carb) actually made the revs go up after a certain point instead of down like I would have expected. Is that normal? I figured less gas would bring the revs down.

Thanks for the video. What happens if you run the wrong setting for too long will it cause damage to your engine ? Too lean or too rich ?

I took off my carburator to clean it took it all apart put it back and my atv don't start any more and the problem is that I didn't measure the turns how do you measure the brass if it don't start you said it needs to be a hot temperature

great video, I dont know if i need a bigger jet and what size it should be for my 82 sr250. the carb has the idle mixture screw on top. I removed the air box and put an pod filter. she backfires and when i accelerate she bogs then picks up then slows again. could it need a bigger jet? You are correct I have saved by rebuilding the motor myself but I have asked a lot of questions.

Matt, Thank you for a very concise, strait forward explanation of the system. I enjoy your videos and look forward to following you in the future. 😎

Yes, it is a 76' XS360. I also had a hard time sourcing carburetor parts for this model. I actually had to get parts from multiple vendors to rebuild these carbs. Let me know what parts you need and I can't point you in the right direction.

how you meant to turn the screw when its underneath

I'm not sure what you mean? The screw I am adjusting meters fuel.

Great job, I've watched a lot of videos on carburetors and finally I have one for the basics that I can save to my favorites list, you nailed it!

Can you help me out I have a full wheeler that was idle fine but would cut out at Full Throttle so I put a new carburetor on it I'm doing what you're showing in the video but when I turn my screw in words it revs up too much.. Its getting way to much gas, when I turn it out to idle it down it dies. It's like there is no perfect spot, I'm either to high or 2 low.. Cant find the right spot no matter what..

Basically bike starts choking when throttle is full open and switching off itself on low rpm.Today i find out two cracks on spark plug so maybe that is the reason?Will see,im waiting for new plug.I will check oil too and i will let you know.

Your biggest concern will probably be the main jet. I'm not familiar with those bikes. Put the pipe on and see where your fuel screw ends up. Also do a plug chop for main jet.

great video dude, thanks for the real deal explanation. now that's what i'm talking about!

Great info and explanation. Thank you.

Hi there,i installed a set for Suzuki xf (oem) working great but doesn't start cold easily...when get warm start instantly.. please help

What did you down size the pilot jet or the main jet

the idle screw on my bike actually fell out, and i had to check this video to make sure i had retuned correctly, particularly because its a big single

Great video. Very easy to understand. Thanks for the info.

Hey Matt great video i think you answered my question with your video! I recently broke down my carb on my 4 wheeler and took it all apart to clean. when i put it all back together it would not idle down, i did not count my idle screw when i took it apart I thought it was going to self destruct, very high RPM, could the idle screw cause this? Thanks for any reply!

Good on you mate ,well expanded, now i know exactly how to do it thank for that

I have a post on performing a plug chop on my website. Check it out. Basically, you need to have the engine run for a few minutes on the carb circuit you are tuning.

i took the carbs off today and cleaned them,,the metal thing covers the choke rod that hooks to all the carbs,,my pilot screws are in front of eatch carb on the top,,and my needle valve has a c clamp holding it in??

Are these adjustments only meant for idle? I have dual carbs idling well, but seems to run rich around 3500rpm once I get going down the road. Thank you!

Great work Matt as usual! Quick couple of question's when my 01 KX 250 get's warm the idle goes down to a stall (cleaned carb completely with a good carb cleaner) every time. I have to increase idle every ride. Also i'm only getting 4-5 hrs out of a new plug before fouling? Also the KX don't run on iridium plugs(won't kick start at all) no more only runs on NGK B8ES 2411, it's like the spark is very weak. I did fit V-Force reeds.

Great Vid. Thank you Sir!!!

No problem!

Here because my bike started to bog down when accelerating specially on up hill. Revs remain high but jts slowly going down, engine losing power and if I continue engine will shut off... Already cleaned the airbox and out a new air filter. Will try replace the spark plug. If still nothing its probably an carb issue Rich bog perhaps? Fuel running to rich?

its a 1995 yamaha yz 125. engine is stock but it has an fmf fatty expansion pipe and pro circuit silencer on it.

my 125cc 4 stroke dirt bike sounds like a 2 stroke and the idle is super high

I have a question my bike when I kick start it starts to idle really high rpms and I’m not sure what to do

I have a 1987 yamaha big bear 350 4x4 could u help me with turning my card cuz I never did it before and I just want help ill video call u if I have to

Can i just leave the fuel screw at less than 2 turns (mine reaches peak at 1/2 turn) instead of leaning the pilot jet? Anyway, factory setting is at 2-3/8 with #38 pilot. And this particular 115cc scooter is well known for its poor mpg. Now i know why, thanks to you.

Hi Matthew. I have the Suzuki EN125-2A with Mikuni BS26SS carb. Pilot screw (fuel) is set as per factory settings which is 2 & 5/8 turn out. And the manual says idle RPM should be anywhere between 1300 - 1500 RPM. Sometimes the bike bogs when given full throttle in 3rd, 4th and 5th gear from 6000 RPM to redline. Below 6000 RPM it runs good. No vaccum leaks, new stock air filter and spark plug installed. What can be the issue? Can it be too lean? The only screw to adjust idle is the screw that hold the butterfly valve slightly open

What of the bike revs when you start it and you have to cut it off because it revs too high? The throttle seems ok it on the handlebar

Excellent description, doodle bug is gonna rip now , thank you

I you make it richer will it go high idle and then drop back down to sounding normal wherein that case you would make it way to rich but Will idle normal ?

Hi, I have a question, you synchronize mixrure screw at the same time ??? Or first one, then the other ?? you know how many turns is for the XS400 ?? thx

Do I have to let engine warm whether the screw is air or fuel? Thank you much. God bless

This really helped me! Thanks!

Mat. I have a 1980's Yamaha XS250 which Im trying to convert the air box to pods. I find the pilot screws dont do much. Its running into high revs off choke

Hi, how hard i must skruw this tight back when i reapir carburator mine?

Hi, I am having Yamaha XS 250 . Idling speed at cold start around 1000 and it increase up to 2500 after running 30 minutes . Kindly give your comments please .

sounds like one cyl isn't firing you should blled your tappets for your hydraluic valve adjustment if one of far off it won't open either the exhuast valve or the two intake valves. meaning not getting enouh air or choking on the exhuast. i just got done rebuilding my motor.

So you have to do this same adjustment on all four carbs? If one is adjusted can you set the other three the same?

I have a Hyosung 250GT, While riding my bike gives off heavy vapor and it goes through fuel like no other. I opened the Carb up and it's clean... so I was told it was the two screws for my air to fuel mixture... what do you think?

Hey man, I have a semi - automatic honda wave and know nothing about bike maintenance. The engine always cuts out when its idleing, for instance when im waiting in traffic (it happens a lot, I live in Vietnam) and the bikes in 1st gear, it stalls all the time. Somebody said its just a matter of adjusting the carburetor so the ratio of air to fuel in the engine is correct. Any tips you could give me would be greatly appreciated. Thanks!!

Are you opening the throttle really fast while the bike is in neutral and not moving (on the kickstand)? If so, that is not a good test. Adjust screw for highest RPM as shown in video. Go for a test ride and accelerate quickly. If there is a slight bog, adjust to richen a bit.

Hi Matthew, I have watch your vid and it's help me to understand regarding this CV carburetor. Mine is RKV 200, a Keeway brand bike and it using CV carburetor. Currently my bike having problem after I change into a new CV carburetor FOC from the Keeway service centre. The idling seems to be okay when I start then engine, but during my riding, when I engage the clutch, the engine suddenly die. When I released the clutch, the engine is back to normal, and still can go for speed. However, when I stop at the traffic light, my engine die again especially during at low speed when I change my gear to neutral. What is your opinion about this matter? thanks bro!

Thank you!

thanks for this quick tutorial.

you can really do adjustment by ear only on 1 cylinder engine, i wasn't able to do it on mine Ninja 500 a paralell twin. It's just too noisy and i can't determine the sound since it's combination of both cylinders... I simply set it 2 turns out as it's factory spec

If you give it throttle and it bogs ,is that usually a indicator it's to lean . When the pilot air is on the bottom of the carburetor and located between the carburetor and engine?

Bro can you help whats the best adjustment for KLX150 large .. i never attempt to check this carb with mechanics here in phil. Any advices will do sir ..thanks and more power

very helpful video thanks.

How do I adjust the mix your screw on a 2004 Honda foreman 450

Your pilot jet is too small. Take the carb apart and see if someone installed a smaller jet. Actually, check for vacuum leaks first. The bog means that it is lean, you compensated by reducing the amount of air by closing the pilot air screw.