I have had problems with my 04 YFZ450, I have had it die on me many times. I found once that the float needle was stuck shut. Now I have found the airbox full of fuel twice. I think that when I took the float out to get to the needle I bent the actuator that closes the float needle. Fixed that and it started and ran for a while. Now I am seeing fuel come out of the fitting on the side of the airbox. Any ideas?

 

I might be way off here but anyways-

On a briggs and stratton lawn tractor I had the timing was off and it was causing fuel to backfire into the air intake. Is it running nicely? If so then its not timing...