I have a '89 Big Bear.
A couple of months ago when having problems starting it, I noticed that gas was ending up in the air box. I posted a question back then and it was mentioned that maybe my valve clearance should be checked. Well, I finally got around to checking it and had to leave it partially done overnight. The next day the air box had approx. 2.5" of gas in it. It drained in there all on its own, without trying to start it or anything. Previously I thought it was getting in there from trying to get it started over and over again.
Any ideas on why this is happening?

 

you should turn your petcock off then that shouldnt happen when your bike is off. as to the gas leaking in while your trying to start sorry i cant help you on that

 

you got some dirt in the needle and seat

 

So, tear down the carb and clean thoroughly?
I failed to mention that I did do this a couple of months ago and it did seem to help the problem. But now it is back and I noticed it leaking in, even when sitting overnight. It hasn't even been ridden much.
I'll try again.
Any other thoughts?

 

Focus on the float needle and seat, and examine the viton(rubber) tip on the needle closely. If its rough, or grooved, then it probably needs replacement.
And I agree with what was said, and whats in the owners manual, that the gas valve needs to go to off, when the motor isnt running.

 

definetly go through the carb, if worse comes to worse, find a used one or just turn off the petcock.

 

there is an o ring around the seat too...

 

could be a bad float....could be stuck on the shaft pin keeping it from moving...

 

Thanks guys.
I will check and do all of the above.

 

I have had this identical problem on my old 600 Grizzly. It turned out to be the choke. Do not laugh !!! Yamaha uses and enricher, It is not your usual butterfly choke. It is a plunger with a centering pin and a rubber seal when you pull the choke cable it meters raw gas directly into the intake. If the seal does not prperly seat when you turn the enricher off it will continue to feed gas into the intake,

I had filled my Grizzly up one afternoon on the way home from a ride. I then put the quad away for a couple of days when I went to ride it it was dam near out of gas. I always check the oil before riding and thank God I did when I pulled the dip stick the crankcase was full of gas as was the air cleaner box I have no idea what would have happened had I tried to start the quad but I can only imagine it would have invoved a great ball of fire.!!!

Check your choke cable mine was pulled out of the lever on the handelbar this in turn kept the choke fully opened and kept feeeding gas to the intake!!