I got a prop balance machine but i think if you put something through the prop that is about the size of the hole and place it between 2 sheets of glass the heavey end of the prop should face down then grab some sandpaper and sand a little off the end that is down and on the inside of the prop. the flucturation of the rpm's maybe tuning and running the engine in. how many litres of fuel have you put through the motor and what% of nitromethane are you runing. I always use 10%nitromethane 18% coolpower 2% edl