my atc250r isnt running right. its a 1984 atc250r, it had been running fine, then the other day i was driving it and it bogged out and stalled, i tried to start it again but it wouldnt fire, i took the plug out , cleaned it up then tried to start it, it started up very easy and ran fine at idle but when i reved it up it missed and died, ive tried new plugs and it keeps doing it, may this be the air fuel mixture? and how can i fix it

 

check your fuel tank vent, might be building vacuum in the tank.

 

If it is this it should run good all the time with your fuel cap off.......worth a try......

 

check your actual spark plug wire for a solid connection and no shorts