Atv troubleshooting 2010 sportsman 500HO backfired and will not restart. New plug, timing chain looks normal,air intake has no vacuum when turning engine over. Where should I look next?

SOURCE: Atv Troubleshooting

well if the motor is a 4 stroke then it could be many things, like timming,bent or burnt valve,even a faulty coil.
however if its a two stroke a stuck power valve, or a bent or broken reed valve will result in a back fire.
if its thepower valve you need to clean and lube with the higest tempature syn. grease you can find,Gary