To wheelie you want to be able to do it at the balance point not with power. Try learning slow wheelies with 1 foot on the grab bar and the other on the brake pedal. Do it on level grass so if you do come back too far it won't scuff the grab bar up much. Once you learn the bikes balance point it becomes easy not to flip but most the time fear of flipping stops you getting to the balance point and you set it down before you get there