I would see if you can borrow some electrical stuff from a friend and do some testing. The crank is out of whack or something in the ignition is out of whack. They shouldn't kick back, especially with the stock ignition system. If you had a dyna and some custom curves or an adjustable plate set way too high I'd say maybe, but with stock components, it shouldn't happen. Do like n20 suggested and check your crank, then I'd try a different CDI, Stator, and flywheel.
I have a couple adjustable timing plates and stators. I'd make ya a good deal on one of the adjustable ones if you want it.
- Jared