The Single Most Common Carburetor Problem (Clogged Pilot Jets) and How To Fix It | MC GARAGE
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- Опубліковано 6 лют 2025
- There are a LOT of things that can go wrong with carburetors, but more often than not running issues (like hard starting, bogging off idle, or a hanging idle) are caused by the same issue: the pilot jet. This video isn’t a comprehensive troubleshooting guide (that would be an hour-long episode), but it does address the single most common carb issue. Hopefully it helps you.
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A motorcycle carburetor is just a mechanical mixing device. It mixes gas from the float bowl with air passing through the throat in a precise ratio, and if that fuel/air ratio is off, you're going to have problems.
Far and away the most common problem carb problem is clogged pilot jets. The pilot jet, along with the mixture screw, are what make your bike run at idle on up until about quarter throttle, so that’s where you should look if your bike is hard to start or only runs with the choke on, bogs or stalls as you crack the throttle open, or has an idle that revs up on its own or “hangs” at a high idle before settling down.
All of these issues are indicative of a lean running condition, meaning that fuel/air ratio has too much air and not enough fuel.
More likely than not your pilot jets are jammed up with debris or gummy gas, and cleaning it means pulling the carb or carbs off your bike. Then you’re going to need to pop off the float bowl and clean the pilot jet, which is typically the smaller of the two brass jets visible on the bottom of the carb. Often it’s removable, so you unscrew it and blast it out with solvent and compressed air.
While you have the carb off your might as well give the thing a thorough cleaning, so click here to see our MC Garage video with step-by-step instructions for a complete carb cleaning.
So why is the pilot circuit such a common problem? Because it’s got the smallest passageways in the carburetor, so they’re the first to clog. Pump gas now has a bunch of ethanol in it and it starts to go bad and gum up in just a matter of weeks, so if you’re not riding your bike regularly you can save yourself a lot of trouble by adding a fuel stabilizer to keep the gas from degrading.
There is one other thing that can cause a lean condition at idle, and that’s an air leak. If your bike has rubber intake boots or relies on an o-ring or gasket to seal the carb to the flange or the flange to the cylinder head, that’s also something to check. But the majority of the time, it’s just an issue with the pilot circuit.
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![How To Tell If Pilot Jet Is Rich or Lean [Jetting Symptoms]](/img/n.gif)
Good video Ari, but I do have 3 comments:
(1) When spraying carb cleaner through the pilot jet make sure that you do a couple of sprays with your finger over the bottom exit hole so that you can make sure the side holes are also clear. You want to see a nice strong mist of solvent coming through.
(2) If the jet is completely clogged often no amount of solvent will clean it. Before I pull a carb for cleaning I hit my local guitar store for a piece of steel E string . They will usually have some left over from stringing jobs and will typically give it to you for free. This is very fine but very stiff wire and you can gently work it through the jet without damaging it. Once there is a passage through the jet, the high pressure cleaner will then remove the rest as it passes through.
(3) I HIGHLY recommend holding the jet in a towel before you blow compressed air through it. Often your fingers alone won't hold it strongly enough and you can blow it across your garage never to be seen again (ask me how I know, LOL).
wouldn't it be easier to soak the pilot jet in a solvent, such as even rubbing alcohol?
E string smart!!
Copper wire works fine
@Mada-yq5sf I have found copper is to soft to work through really crusty clogged jets. Guitar string works better. But to get the last of the residue I like blasting carb cleaner through.
Cool stuff
When blasting out your pilot jet, hold on real tight so it doesn't go shooting across the garage and land behind the impossible to move workbench.
Wish I saw this comment earlier...
Why would your impossible to move work bench have gaps things can fall into ?
That's the real question
Hi there I'm from South Africa need some advice I'm not sure if it's the carbs but when I start my Suzuki bandit GSF 400 and it's warm when I begin to pull away and I open it to 6 thousands revs it then drops to 4 thousand revs then it jumps to 12 or 13 thousand revs why does it do that it's like when I want to pull away and open the throttle to quick the bike dies I have to open the throttle slowly to ride fast or pull away how can I fix this ? Thx
Sounds like he knows this from experience...
Quintus 😂
This video series is great. In fact, the worst thing about it is the time between episodes
I just found this channel yesterday, watched about 6 hours worth of content so far. Your videos are insanely well done guys.
Thanks man, I am! Im a new driver, got a 00 bmw f650, and been having a lot of trouble with clutch linkage adjustment and hard shifting.
If I adjust cable to far out on handle shift lever, easy shifting but clutch slips.
If I adjust cable to far in, clutch slips still and super bad shifting.
Been too afraid to adjust anything where cable connects to arm below on engine (I dont know what thats called). Theres a sweet spot I guess for easy clutching vs slip? I have it set right now to where its hard shifting, but no slip. If this is a common thing can you do a vid about that? That'd be epic man. Or just bring anything else coming, Im sure I'd watch it! :)
Thanks very much for the reply sir!
@Ari! Can you please do an vid on replacing forks seals!
Mine need done, and I'm hoping I wont need to pay a shop to do it.. :/
Thank you so much for this video! You saved me more hours of figuring out what was happening with my Honda Dominator, that it just didn't start (only by using starting fluid). Checked almost everything (fuel, spark, battery, measured stator, pulse generator, coil, electricity contacts, CDI box contacts, vacuum leaks around carb and air box, etc.), especially after disassembling and cleaning carb. In the end your video made me think that it still might be a carb related issue, because I started to remember that the problem started when I switched the fuel tank petcock to RESERVE. Removed the petcock and yeap - there were some debris on the bottom of the tank, without original fuel filter, which clogged the pilot jet. After blasting out the pilot jet with an air gun and assembling everything back together, Dommie now runs just great! Thanks!
I have a honda rancher 350 that will only run on staring fluid.
This video was not “very brief” it was informative and not too long. Usually these videos are unorganized. This was not too long. Keep it up ! 👍
"...or the bottom."
Smooth.
lol notice it too. how it suddenly falls on its back lol
scary, somehow
Lmfao 😂😂😂 Im dead
He a smooth operator 😂
I replayed that several times.
I've been intimidated by how complex carbs look for a long time, but this video was very informative and I definitely have everything I need to clear out my pilot jets
Thank you, gave me the confidence to give it a try on my 4 inline carb, removed it all and followed it to clean the pilot. Bike started and held idle fine, so happy!!!
Ari, thanks. I really get benefit from your clear explanations. I have a 1984 Suzuki GR650 Tempter. A bit of an oddity, but then so am I at 66 years old doing my first more in-depth build.
I am doing some performance and styling mods on the Tempter. Carb, exhaust, and air box work, is key on the performance front. I definitely had some high hanging idle with no sign of air leaks at the engine-side boots. Most of the problems seemed related to the pilot system.
I've rejet'd the pilots by one size, raised the needles by one notch, and rejet'd the mains by three sizes, to work hopefully well with the new more open mufflers and opened out air box. Of course I cleaned the carb interiors while at it. Fingers crossed :-)
Any updates?
@@Johnferrana I've sold that bike long ago, but fyi, the aftermarket main jet was much too rich. Had to be downsized. Other than that it ran awesome.
Thanks for the video. I have cleaned many pilot jets and never have I only had to spray cleaner/air to clean them. LOL. When those symptoms occur, It's usually HARD deposits restricting the hole or plugged completely. Have to clean with a small wire, or jet cleaner tips, etc. Jets are cheap, but seems I never have them on hand when needed! Just yesterday, out of the blue, my reliable Vulcan 800 wouldn't idle. Pilot jet was almost closed completely with hard black deposits. Took 15 minutes to clear. Thanks for the videos!
My just rebuilt 99 ZX7 was running like a dream for a few months, but now it runs poor on low revs. Gonna check that pilot jet . Thanks a bunch
My VFR400 was notoriously bad for this. Great video! People should really watch this and learn.
thank you for this fan-freaking-tastic video series because of this video series you have given me the confidence to perform maintenance on my motorcycle that I would normally have to pay a shop hundreds of dollars to do last March I put tires on my motorcycle front and rear 2000 CBR 600 F4 have a motion Pro balancing stand everything went off without a hitch this spring I am going to change the clutch thanks Ari
Good. As an old dealership tech, I've told many people: "80% of the time - DIRT is your problem".
Never really a problem until Mr. Ethnol cam along .
I have no idea what you're talking about but I love this series.
Excellent video! I would like to add (myself being the owner of 30 motorcycles) that fuel with ethanol in it makes the bike run leaner at idle (in the older bikes any way - such as the Kawasaki KZ`S, Suzuki GS`s and such). Pretty much every bike I own, I have turned the idle air screw out 1/2 to 3/4 of a turn for a much better idle. Hope this helps!
Ari, how about a vid on synchronizing a bank of carbs on a 4 cyl? Another good one, and a critical setting, is float height. Again, on carbs for an inline 4. Maybe show the method of using a clear piece of tubing connected to the drain port (usually done on the bench). Love the work you and Zach do on this channel, keep it up guys.
I have a 1974 CL360 and that is exactly what is wrong with my bike! Super helpful video. Thanks!!
Spot on. The leakge in intake manifold rubber to engine head is very notorious. Also the mouth of the part that is locking with engine head should be properly screwed (using gel sealant in most cases)
Leakages should be taken good care 👍🏻👍🏻👍🏻
Thank you so much! This clears everything wrong with my bike and it worked flawlessly. I’ve never seen a “perfect” tutorial but this covered absolutely everything needed!
My first step with a poor running bike is to dump a bottle of seafoam in the tank. A good portion of the time, that cleans the carbs nicely and I don't even have to take anything apart. That and a good carb balance every once in a while are all I've done to my '85 CB650 carbs.
The Single Most Common Carburetor Problem = THE OWNER!
fwh79 what if you bought a bike with a problem
@@calebkroll4698 Previous owner
Of quality of petrol?
@@lynnmckenney1987 ALWAYS
an owner whos a squid and always on high RPM
i have all this problem, i do step by step like your video and now she run like a new! i'm so happy, thanks. :) 1994 suzuki DR125
I'm having this in my Honda Trigger 150. When I open throttle, the engine goes off. But I failed to repair as per your information. But your video gave me the idea how to fix it. Thanks.
I just now found your video and it helped me greatly it was indeed a clogged Jet and passageway for the idle!.
My bike's would only run on food show and everytime I give it gas it wouldn't either rib out of control a title or die when giving it more air
I wish the title would contain the exact issue (pilot jet clogged) and not just "most common problem". I think descriptive titles are always great and help with orientation in all those billions of youtube videos.
A mighty title for a mighty video :) . Thanks!
Never understood why the fuel and air mixture screws are in an impossible to reach spot. If you're trying to tune it you have to constantly take it off to adjust it. Ugh
Thanks. That confirms what I thought was happening. The main jet I know was getting fuel through but the quad would not idle and I'd have to hold the throttle down to keep it running rather rough. I also tried putting penetrating oil into the passageway to help clean out any clogging as well as carb cleaner. I don't feel air flow through but I'll try a bit more TLC cleaning before I reinstall it.
Perfect, many thanks. Brief videos are great, nothing worse than listening to someone rattling on just to make content.
Great little walk through on this most common issue. Appreciate you man!
Been watching these videos for years ever since my first motorcycle!
Thanks, directly on how to fix the problem, no five minutes of talking :)
My son 7-year old Tanmay watches and learns from your videos.
This series keeps getting better. ...or the bottom... nice.
Always order a Carbrebuilt kit, you might use it afterall and you don't have to wait shipent time. Give the carb some ultrasonic love.
I watch a lot of how to videos and often the hosts are irritating.
This is not those videos your host does an awesome job.
Awesome video as always. Carbs are the main reason I decided to go with my fuel injected fz6. Coming from a 200cc dual sport and a vstar 650 it's best decision I've made. Can't wait until I get done with college and can get a real bike lol
Great vid Mr Henning .. I just rebuilt my carbs this winter, with confidence inspired by your first carb video ..
Thanks Ari
Biker mike has the solution for really stubborn clogged pilot jets! And it’s real easy!!!
My pilot jet was clog and destroy. I got a 45. Hope it fits and it doesn't do all the crap it was with h you showed us. I'm praying! Lol ty for the video
Thanks for the great video. This almost confirms what I was thinking. I ride a '88 GSX1100F and up until a day or two ago it idled and ran great. I filled it at the shell station the other day (V-Power which I believe is non ethanol) and it stalled on me a couple of times while giving the wife a ride to work today. It runs like crap just at idle and a bit above, but when I roll it on it almost rips my arms off. I'm thinking a bit of crap in one of my pilot jets.
This explains so much about a bike I recently sold... definitely time to pop out the carbs on the SV and see what they look like.
Run a thin wire, like a single thread from a wirebrush, trough the jet. As solvent and compressed air might not be enough. Had a clogged up pilot jet that wouldn't open with just solvent and compressed air. The customer said he did a troughout cleaning of the carb and jets and it still wouldn't run properly. So he suspected a faulty carb and brought it in. An hour later i could call him up with some good news. He had a good running motor for only 50€ instead of 380€ + labor.
I had same experience. 1975 Honda XL350. "Pro" shop carb clean. Died from 1/4 to 3/4 throttle anyway. It was the deeply buried and invisible air jet for the emulsion tube. I stuck a long stiff wire into the suspect hole on front of carb, poking by braille, until I felt it go through. Excitement. Reassembled and it ran perfectly. Happiest day of my life!
Neat to see your name here! Cheers
Holy Crap, it's Randy Pobst /\ , this dudes an awesome race driver!
Hey man...I have a suzuki gz250 and I have been dying on it...I have tried everything and now I'm just in the dark.
Single mikuni bsr32ss and i cleaned it changed jets (same as factory no upgrade) and it will idle but when I crack the throttle it dies out... I'm thinking the passage in the body of the carb is clogged?????? PLEASE HELP I'VE BEEN DOWN 10 DAYS
@@randypobstofficial I have a gz250 suzuki I replaced factory jets and cleaned it...then it did the same thing...idle fine then when you crack the throttle it dies. Do you think I could also have a clog like you did in the carb body
VERY VERY good young man. iam Moe back in the 60s i did a lot carbs. on big American cars. looks like you know what you are doing. keep up the good work.
1:38 that was dope haha
the carb fell over and u played it off smooth lol
That may be the most clever, bumper video / logo animation I've ever seen.
Used to look after 30-40 used bikes on a sales floor , so no time to remove carbs and be cleaning pilots properly ,
one way is to drain the fuel and give the bowl’s a quick short blast of compressed air .. and really short 1sec blasts for CV Carbs or obviously the diaphragm rubbers will pop.
But it works 8 times out of 10.
What about the return springs? Would taking each carb off the rail not enough spring to return back
Thanks Ari! All your videos are great and really helpful
currently cleaning mine on my 2000 Bandit 1216. 164k and counting.. second set of carbs though!
thanks so much. I went to ride my husqvarna tc125 today and it wouldnt idle with the choke off, it kept dying out. I will have my dad help me clean the carb up and get her running again.
Great video. I’m having problems with a virago 535 as in the back carb cannot be made to run leaner so can air fuel jets get clogged up. Regards from England
Great video 👍🏻. I’m having that problem with a keihin fcr on my old yz450, I think my issue is the orifice that the pilot jet screws into though, rather than the jet itself, which I’ve already cleaned with no result. Good job 👍🏻 mate ✌🏻
Z50. Love it. Owned one along with the MIni Trail 70 when we were kids.
Significant Weather change can do it too, anyone riding a Carbureted Bike may have noticed that it just doesn't Run very smooth on Hot Day's.. that's because the Factory Set the A/F in a very mild Climate, and a change in the Barometric pressure can definitely effect a Carbureted Engine.
Love this channel. Ari makes any topic feel like lemon squeezy!
Advise needed for my FTR 223 ! :)
When the engine is hot (after around 10min of driving), I feel inconsistency in 2 situations :
- When accelerating at low RPM : The engine seems to "skip a beat" before the bike actually accelerates
- When cruising at relatively high RPM : the engine isn't smooth, especially in 3rd and 4th gear
It seems to be carburator-related, but any idea how, and how to fix it ?
Thanks a lot !
Hey great video, this may answer many of the issues I have on my 85' Suzuki GS550L;
would a stuck pilot also lead to having a gas leak from where the Air cleaner tube is connected? Some suggest a Sticky Float or another person suggested it may be "valve starter" that is loose due to a stripped Holding cap.
I just LOOOOVEE this MC Garage videos, so easy to understand. thanks... Mr Henning is a great teacher...
Damn Ari, you explain it so good that it almost feels easy to mess with it. Great videos.
I have a knee series carburetor with a 38 pilot jet and I cannot see through it. Should I be able to see light clear through or does this jet use the orifices on the sides?
This resonates with me as I have had constant pilot jet problems with my Kawasaki engined lawn tractor with Walboro LMF carb. Unfortunately on this carb it is nearly impossible to clear pilot jets due to the idiotic design of the carb so on one occasion only a new carb would do.
Did all the cleaning and the bike will hardly run on choke. I do not have the air box on will that matter?
Who else has a sudden urge to buy a 50cc mini bike? :-D
Ari Henning Tempting! However:
1. I'm in Pennsylvania
2. My wife would likely have me sleeping on the couch.
Come to think of it, that couch is pretty comfortable.
me but i bought 750 instead!
Akaash Khokhar me just bought a 1000cc project bike as my firat
was given a 71 z50 by a coworker as a gift and it needed work. upon more inspection i realised he swapped the 50cc motor for a 125.... the front wheels will always come up in second gear lol i love that fucking bike
I’ll be buying my dads beat up xr75 and fixing it up over the summer :)
Awsome video, I have a 98 Valkryie and half the jets were just like that. My question is, how do you check/adj the fuel mix screw on a multiple cyl bike?
Thanks for not replying to my question. The answer was in the video. Duh!
Hopefully i can get help here
I have an 01 zx6r idles fine but wont go over 40 feels like a fuel issue checked the pump cleaned carbs changed gas and spark plugs nothing worked took the bike to get looked at only to pay 115 for them to tell me change the fuel filter😒 i drove it home decided to remove the airbox and drove it down the street problem went away and it worked a few days now the problem is back weirdest thing ive seen any ideas of what im dealing with
Bike wouldn't start this morning. Same symptoms as shown on the mini bike. I had the tank off last week, and i guess i didn't clean the tab before reattaching the fuel line.
Wish me luck
Did you guys go to Phillip Island for the new GSXR? Just curious if you have a video or article in the works.
I already cleaned my carb thoroughly, I took extra time with it. I still have an issue with it, if I slow down the wheel, the engine slows down, and then dies. Valves are good everything is good, not sure if the clutch is sticking? I'll be replacing it in a couple of days. Going back to the carb? Maybe there's one hole the blow gun cannot blow out? I think I'll just get a extra new carb just in case, they are cheap in price. Forgot to mention the air screw doesn't do anything.
How much does it roughly cost to get your carbs cleaned from a pro ?
Hello, Ari.WE love your videos with lots of information..keep em posting. WHEN CAN WE EXPECT A 2017 SUPERBIKE SHOOTOUT. ????????????
What if my bike runs great till I run at 55 for little while then gets sluggish and backfires a little and preassure coming from air box and no power ? Fuel pump ? Not getting enuff gas ? I can let it sit for a few and it does good again?
I wish I could have you work on my ke100. Haven’t riden it in over a decade and rebuilt it and still nothing.
ah crap, i never thought of the ethanol issue, thanks for this video, very informative and i learned something ! Merci.!
could you please make a video of your rc390 race bike !! about what modes u have done on it, what one needs to take care while preping a race bike, what should one look for while buying a aftermarket parts ! your video will make alot of difference. please do one !
If I unloosen the mixture screw, will that enrichen the fuel mixture, or enleanen it?
I have a 50cc that hangs after i let go of the throttle with all 3 carbs ive tried on it. 2 new, 1 old and cleaned. New intake gasket too. I think its a vacuum leak, but where else do I have to look if the intake is all sealed up and good?
Can the wrong air and gas mixture cause over revving?
Hi, My bike's throttle does not stop even after the fuel screw is tightened to it's fullest extent, Can you please guide what could have been the problem.
Does that Motion Pro tool work really well? I bought a different brand with a ninety degree bend and it's very difficult to get any sense/feel of pilot jet movement. Great videos
Thank you. You covered my specific issues
thats the thing about carbs like i got a 99 r1 with a set of carbs i cleaned, left it for a month in the garage and now it took for ever to start had to spray some flameable spray into the airbox to get it started, gsxr 600 impounded for like 3 months and started right up and ran perfect straight away... got to love fuel injection
Having a lot of trouble getting to the bottom of an issue.. I have an 84 Yamaha Venture 1200, it's a V4. While my Airbox lid is off it Idles normally for the most part. But the moment I put the Cap on it instantly Revs to around 5500 RPM. This happens without the throttle Butterfly's moving in any way. Ive completely cleaned the Carbs, Re-seated the Intake boot's and spent hours searching for Vaccum leak's with no results. I have no idea what's going on here and any suggestions are welcome...
Thank you ! I think this has verified my boat problem !!!
how can you remove a idle mixture screw needle that is broken off and stuck in the carburetor body?
What if the scooter runs well but needs a little throttle turned slightly upon turning over and starting? What does that usually mean? Yes it’s got all the typical 70cc big bore upgrades. Kymco people 50 2009....
vary helpfull, thanks. wish I had watched this before completely cleaning everything but the pilot jet, then putting it all back together, ha. thanks again!
I really wish I had found videos like these years ago. maybe i'd still have my 94 Ninja...
want to ask you that I have a 2000 gsxr 600 , I completely clean all 4 carbs and still only run with the choke on only. Also clean the fuel filter, fresh gas. Has no idea why. Do you think is the mixture screw, Maybe you can help me out.
is there a effect on the bike engine, when you remove the air filter/air cleaner ? it's common here in my country especially in mc underbone and scooter tuner. I don't know the right term but they used to call it "OPEN CARB" some put velocity stack on it and others just a open aftermarket carb.
What might cause my bike to just rev to the max at idle? Its also pouring gas out of what i think is the crankcase vent tube. Any info will help thanks
Hi ,
My bike is having some problem which I tried getting fixed by many mechanics unfortunately the problems still persists my carburator slider frequently getting clogged with carbon and after a few kilometres accelerator will get jammed also the air filter which 2 days ago I had it replaced is also having carbon deposits on them and has a petrol smell on them how to diagonise the issue? Sometimes white smoke comes out of exhaust. Any advice????
Why would gas be getting into the diaphragm area where the cover is? I have a 95 Yamaha Virago 535sg
My motorcycle has this switching on only with the choke and turning off on opening the throttle. Once I cover about a quarter of a mile with the choke on it becomes normal and remains normal for the rest of the day(even after switching off and standing a couple of hours). If I clean the jets and put them back on(before starting the bike for the day), the bike starts great for that day, but the next day again it is back to the same issue with starting. I use copper wire to poke the jets as copper is supposed to be softer than brass, so I guess that is not an issue as such. Else, I use white spirit injected into the jets with a syringe to clean them. Still I end up with the starting issue the next day. Do you think it is time to replace the jets?
Good video and right to the point. Thank you good sir.
Hai MC My scooty suziki access 125cc. Idealling is perfect engine starts in one kick but when i raise throttle engine is hesitating & stalling exactly like you shown in this video. This stalling problem belongs to which jet.
Would you do the difference of single sided swing arm vs conventional one?
Did u contracted a gnome or a pixie to make the 1:40 movement?