carb or timing
If it is backfiring only when you kill the engine, allow the engine to idle a few minutes before you kill it. If it is backfiring while in use, check the intake gasket and bolts for wear or looseness.
water in gas or out of time change the spark plug and check the carb bowl for water if there is then drain the tank and clean the carb Additional comment: Often when you have a motorcycle or ATV that is backfiring you will find that your bike is having a problem with bad spark timing. This will also cause your Jerking... Take your bike to a profession and have them look at the carburetor adjustment and the timing.
To prevent backfiring make sure the belt is tight and in good working order. Also clean the air filters regularly.
If it is backfiring the timing is set incorrectly or the spark plug wires are not connected in the correct order.
Backfiring.
The best answer for this is: Get a tune-up.
backfiring.
Probably. Backfiring is a symptom of a lean condition. Wouldn't want to leave it like that.
Needs a tune up
advance the timing a little.
Yes.