Motorcycle and ATV Carburetors 101 

Glad you got something out of this video and we appreciate the feedback. Thanks for watching!

@@rmatvmc hi I have a 2002 trx400ex can i put a 36mm cr500 carb on it..will it run??...plz respond

@@jayvlogs5544 It might run, but the carburetor is far to big for the accurate fuel/air ratio that the engine needs.

That's what we like to hear!!!!!!!

the accelerator pump is adjustable through the leak jet among other details as well

You need to check the fuel valve on your fuel tank to see if its clogged. some valves you can rebuild some you cant. but if you pull the fuel supply line off the carburetor and the fuel valve turned on and no fuel flows then that is the issue.

You need to ride more bikes, son

@@postmortemspasm sorry if an old fart like me cant afford the new fangled technology.

Check the Hot Start lever adjustment. But for the most part your bike needs to be tuned to you elevation and riding conditions by a good mechanic. The other issue that might be going on is your intake valve clearance adjustment is tight causing the intake valves to not seal correctly causing compression to push back into the carburetor that will not allow the fuel and air to be sucking into the combustion chamber for internal combustion to happen.

It's not the return spring, its the cable being corroded and lack of lubrication. Try a new cable and see if that solves your problem.

I'm not sure you can call that uncorked. If you are wanting more air flow you can do that and yes you most likely need to go a bigger size in pilot jet. First I would adjust for elevation in your jetting, that might make all the difference in running conditions that you are originally seeking for.

You are correct and incorrect. Yes you loose air volume as you get higher in elevation which will both cause a richer condition, but the lose of air volume will effect it. The very reason that the pilot screw/fuel screw/air mixture screw or whatever you want to call it is there for adjustment along with the idle screw. Barometric pressure, and humidity also effect it causing a lean or rich condition. If you were to look at it on a chart, the lower elevation you the changes in jet size are less dramatic in running conditions than it would be at higher elevation because of less air. You can over rich or lean one circuit and try to compensate for the lack of correct adjustment of another circuit to a certain degree. But its not accurate and your engine will never run the best it can without adjusting everything properly.

you got it backwards. higher elevation is less air. so less fuel at higher elevation. see? for what it's worth i've seen the tendency for some folks to think that at higher altitude you need to add fuel and i can't understand why some people think this.

Thanks for the positive feedback!

Check your valve clearance. If your intake valves are tight with no clearance than that is your problem.

stvnmoto, your suggestion was exactly correct. I happened to adjust the valves a couple of weeks ago just hoping it would help and I noticed that one of the intake valves had no clearance. After putting everything back together it started easily with the e-start and no throttle. My subsequent rides were great. Thanks!

Hi Jeaven. It can be normal to kick it a bunch of times, especially if its cold. If it were mine I would adjust the low speed fuel screw and turn it out 1/4-1/2 turn to richen up that circuit. There might be a tamper proof plug installed in the way of the screw that may need to be drilled out so you can adjust it, but that's the solution to your issue.

Do you guys sell two-stroke carburetors for quads I have a 250 Polaris looking for a carburetor for it

If you have backfiring happening you'll want to try advancing your timing. Also, check the fuel filter and fuel pump if you have one.

well if the original rebuild-able carburetor is gone maybe another chinese copy will be better a 2nd time

It's a Utah thing lol

Just had same condition on 200 Yamaha. Mine would not get past idle with throttle unless on choke. (Completely clear pilot circuit) my fix was going 1 size up on pilot jet. Make sure your new Chinese carb has the same jets. It may have smaller as they are usually geared towards 125cc or less machines. Good luck let us know your fix!🤞👍

Don't buy Chinese carbs! they are junk. you are better off rebuilding the OEM carb.

Check throttle cable free play and adjust the idle screw down.

They are either for a TPS sensor or Electric choke.

That's a good idea. Thanks for the suggestion!

You will most likely need to rejet any carburetor for your specific riding conditions and elevation.

Check the float valve and O-ring on the float valve seat. Most likely the cause.

We have carburetor repair kits for your ATV that you can check out here: www.rockymountainatvmc.com/parts/atv-fuel-and-air-intake-systems?v=2006-suzuki-eiger-400-4x4

If anything is in the carburetor it will most likely not run very well. You will want to do a thorough cleaning of the carburetor.

@@rmatvmc will that require taking the whole thing apart and putting it back together?

You'll want to bend the tang up towards the needle, which will in turn allow your float level to be set lower. Unfortunately, we don't have a video on setting float level but there are some great videos on RU-vid showing the process.

Rocky Mountain ATV MC thank you very much. Out of adjustment will explain what I meant ones correct?

You need to rebuild or replace your carburetor. The 660 carbs have a vent to the atmosphere that would allow dirt into it and trash the slide and carb slide casting. It was a great machine but bad flaw.

The stock carburetor on a 1990 Suzuki LT250S should be a Mikuni 34mm.

@@rmatvmc We had it messured they said it was 32mm it is a round slide

Could be. Sounds like the main jet might be too big. You can verify by trying to rev with the choke on, stays the same or worse=smaller main, better=bigger main. Then with choke off and air box lid off, rev it again, better=smaller main, worse=bigger main. This is assuming you've checked all the basics (fresh fuel, clean air filter etc.). For reference, our QA Parts carbs that fit your ATV come with a 120 main and a 45 pilot. If you can't get the carb you have ironed out, I'd try the QA Parts carb and be done with it. -Charles

@@rmatvmc thank you I will try this

Good luck, let us know how it goes!

I think nobody knows, because i never see an answer to this question.

as far as I know, it is used when you start the bike. at that point you need only fuel to get through and so you "close" the air stream. after the engine has started, you let again the air mixed with the fuel. I hope I'm getting that right...:)

I believe you are referring to the TPS (throttle position sensor).

@@rmatvmc yes it is on the opposite side of the throttle thank you! I have trouble getting the right ratio on my scooter.. its 4stroke and have only one mixture screw, how do i know if its working properly?

It will depend on your exact engine but the idle speed will generally be around 1,100 to 1,500 RPM.

@@rmatvmc This is a bike with only 2000 miles. The idle was 1000 rpm. The headlight would blink at 1000 and would not start electrically. The battery would go dead so i turned it up to 1300 so the headlight stays bright. I think the problem is fixed but if in happens again i will replace the battery. Thanks

If you are running too rich and have already maxed out your adjustment screw, you need to get a smaller pilot jet to reduce fuel flow even more. Vise versa. If you have already backed your adjustemt screw all the way off, and are still running lean, then you need to get a bigger pilot jet to let more fuel in.

I just rebuilt the carburetor on my atv and it was running super rich. Black spark plug, wouldn't run well after it warmed up, and would bog at full throttle. I had to fully close my pilot adjustment screw. Luckily mine works when fully screwed in so I don't have to replace the pilot jet.

It must be lean move the clip on the needle

Downward is more rich on clip position

Dosalt please explain your point

Had to show off that clear float bowl ;) Good eye. Thanks for watching!

Should have explained how that bad boy works.

I would have but we were trying to keep to the basics of carburetor function.