What causes an ATV to backfire and jerk when you try to ride it?

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.