ORIGINAL: controlliner
The timing on the crank inlet port is advanced more than most engines using an airplane prop. You would benefit using a smaller prop on the engine with more pitch, to get in the engines RPM ''sweet spot'' let it wind up.
This boat comes with a 9x7 APC pusher prop I believe. As I recall from another forum, this .27 is timed like a car engine. High exhaust timing and aggressive intake and transfer timing, so it should rev. It is probably lugged down with a 9x7 prop though. I'll have to find the link when I get off work.