B & S 6.5hp INTEK timing?

I have a log splitter with a vertical B & S INTEK engine and it some times acts like the timing is off when you try to start it. It seems like it fires too early, and the motor spins backward and rips the recoil handle right out of your hand. There is no pattern to this happening....you just start to not be leary any longer and bang...no more callouses on your fingers.