i have 2005 sportsman 500 H.O i am working on for a friend. he was riding it and it blew the plug out of the head did not take any threads with it so im thinking it was just loose and worked it self out. after that it will not run i finally got it to start after a while of messing with the throttle. if i time it just right i can i can get it to start have to have it at W.O.T to keep it running it only runs at aout 300rpm will not rev up as soon as i let off the throttle it dies and backfires out of the carb. i have tried everything i can think of. please help im beating my head against a wall with this thing. than you in advance..