If you have a tach, look for at least 12,000 rpm on a 10" or 11" prop. I would bet that with a 12-7 prop you will be under 10,000 rpm which just won't cut it. I would suggest go fro a 10-5 or 10-6 prop with that engine, no more. APC are more efficient bbut alos load up the engine at higher throttle settings so expect lower rpm numbers with the same prop size and pitch.[8D]