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Please help, gas in airbox

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I have a yamaha YFM200 4 stroke ATV.

I cleaned out the carb, put it all together and she has been running great. I start and ride it once a week and have had no problems at all. 2 weeks ago I went on an ice fishing trip, I started it up Friday night and drove it on to the truck without any problems. Saturday I drove it off of the truck, drove it out on the ice, it stalled, and would not restart. I towed it in, took it home Sunday and still it would not start.

Upon checking the airbox I found that the whole tank of gas, all of it, had drained into the airbox. I took off the carb boot so the carb had fresh air, put gas back in the tank and she started right up. I then took the bowl off of the carb, turned the petcock on and moved the floats up with my finger to make sure the needle valve closed, and it all seemed to work properly. I drained all of the gas out of the air box, dried it, put the boots back on, air filter in, reassembled everything. She started right up again.

10 minutes later the same issue, she stalled, wouldnt start, and upon inspection I found the airbox filled with gas again.

What could possibly be my problem?

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Float level is too high, my guess. I've had some change for no appearant reason, with out any human intervention.

Aside from that, gunk/debris in the gas which is holding the float valve open.

Last, you have to replace the float valve.

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Thanks for the fast response. The float valve isnt old, and like i said I watched it shut off while I raised the float with my finger. So what is my next step bend the little prong to lower the float level? and that should fix it?

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That's what I would do. Small adjustments, a degree or two can be the difference between just enough and too far. It's often a pain, what I've done to save myself hassle is bought a ordinary lawn mower petcock, about $8 with fuel line, connected that to a funnel. That way I can bench test the carbs with gas for a too-high float level, but too-low still requires putting it on the bike and running it including some WOT for a bit to see if it starves.

Two things to keep in mind with your method of testing.

First, you will exert a lot more force on the float than gasoline does. I don't have a volumetric weight on gas, for some reason I remember 12 lbs per gallon, but the floats displace maybe five ccs of fuel. How much does five ccs of gas weigh? That's how much force the floats exert against the valve. You could still have dirt holding the valve open when assembled even though it did close when you used your finger.

Second, you are raising it all the way up, the float may not reach that point depending on all the other variables inside the bowl.

Another thing to keep in mind when testing the way you did, is it's likely you raised the float level even higher by pushing on the floats. Most people turn the carb upside down to determine the float level, although I'll admit it's a little more difficult to determine if the valve works or not.

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OK Boys - again thanks for the detailed responses.

I took apart the carb and made a large adjustment (in perspective) on the float level and what I ended up with was no gas at all. I then tore it back down and found a happy medium where the floats should sit, and that seemed to do it. The bike now runs great, idles great and i ran it for a while (riding as well) giving it a lot of throttle and it isnt starving. I let it sit idleing for 30 mins to see if it would flood or drown itself out which it did not. it restarts no problem as well.

All fixed, and thanks again.

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Sounds like a leaky petcock from the gas tank, which is overflowing into the the carb and then backing up into the air box. You may be lucky that you haven't gotten hydrolocked. If a lot of gasoline gas leaks into a cylinder and you go to start it, that cylinder may go to hell on you. Also, the only other place to look is in the float bowl. The floats may not be shutting off as they should, for whatever reason. Usually gunk!

Check your oil dipstick and smell it. (You do smell your oil every now and then don't you?? ) If you smell gasoline.....change the oil right away.

Meanwhile, check to be sure that petcock isn't faulty. That's the best place to start.

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im not sure if that petcock is vacume operated but if it is that could be a thing to check.if a vac operated petcock goes bad it sometimes dumps fuel thru the vac line into the intake

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OK Boys - again thanks for the detailed responses.

I took apart the carb and made a large adjustment (in perspective) on the float level and what I ended up with was no gas at all. I then tore it back down and found a happy medium where the floats should sit, and that seemed to do it. The bike now runs great, idles great and i ran it for a while (riding as well) giving it a lot of throttle and it isnt starving. I let it sit idleing for 30 mins to see if it would flood or drown itself out which it did not. it restarts no problem as well.

All fixed, and thanks again.

Glad it worked.

I've done that too, go through all the trouble of tearing everything apart, put it all back together, only to find there's no gas at all!

I should have mentioned that in my bench test method, I turn the gas on, wait for a bit to see if it overflows, then open the drain on the bottom of the bowl to ensure that there is indeed some gas going in. However, checking for the correct "medium" setting really requires riding the bike.

Good job, you probably saved yourself $50-100 depending on your mechanic and how difficult it is to remove/reinstall the carb. (On my street bike, they are a royal pain in the ass, it takes a good 20 minutes to remove and usually a half hour to reinstall everything you have to remove to take them out. On my DS, it's about 10 minutes each way.)

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Yup shes all set now and thanks.

Also the petcock is just a gravity flow, and I checked it to make sure she was shutting off completley when i had everything apart.

Shes all set now. thanks again fellas.

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