I have to agree, spinning to the right is trying to start it backwards. I would forget the impact driver as that's asking to not only destroy the engine but is asking to get hurt. If you installed a grooved flywheel on your engine, I'd use one of these, making sure it spins counterclockwise when looking at the prop from the boat's rear:
http://www3.towerhobbies.com/cgi-bin...?&I=LXJC35&P=0