start problem

Okay, so I've taken apart most of the engine to try and find the error, and nothing has worked. It's not even close starting, the only sound is the engine turning from the starter. Thing I've done: Cleaned out the carburettor several times just to make sure. Also tried spraying starting fluid...

I was riding my quad one day running perfectly no problem. I put it away and no problem at all the next day I go start it up it sounds normal but 1 minute into it warming up it just dies. Well I start it up again and lay a little on the throttle and keep it in one spot and the rpms go down and...

went riding for a few hours and toward end of my ride quad would big down and almost did out after half throttle. Took carb off checked float looked ok, changed plug, started up and did same thing. In addition now when gas is on is pisses out the overflow of carb and now won't start like there...