sounds like a bad rectifier.. The stator makes the spark in a bike with kick start(no battery) however the stator aka magneto makes ac power but the spark plug needs dc power so the rectifier changes ac to dc (or visa versa, to lazy to think intently about it).
Ur stator could also be at fault. I fried the stator in my Raptor and it would still run but it would back and run poorly.
BTW.. for those who dont know... Im a certified atv and motorcycle repair tech.