my cousin has a 350 big bear with mikuni carb.When he runs it for a while and shuts it off gas keeps running and backs up into his air box.The float looks like it is ok.This quad has sat for a while and the bowl was tarnished.The diaphram is really flexible and out of shape.Would the diaphram not working properly cause this.The jets and needle were all clean.This is a all stock machine.Any suggestions would help.

 

come on

 

considering that the quad has sat for a long time, presumably with the same fuel in it, I would first look at the float valve. the float tang rests on it and if varnish has caused it to be stuck open it won't shut off the fuel when the bowl is full. Try spraying some carb cleaner on the valve and let it remain awhile before blowing it with compressed air; then gently lift the flote and lower it to see if it is closing the spring loaded valve. If you have to replace the valve, it's advisable to replace the valve and valve seat as a unit.