You might want to appeal to .....................
a little larger audience. If you don't already know about the site, a great number of pleasure boater, tech's, etc., frequent "Scream & Fly", which has been of good help to me regards similar problems with my bass boat engine.
As a previous poster said, sounds like you might have a lack of fuel problem at higher RPM.
Many causes such as clogged fuel filters, bad primer bulb in the fuel line from tank to motor, etc. Sometimes a blocked vent on the tank can cause this type problem.
If you live where the gas is 10% ethanol blend, there are many problems that can be caused by that if the boat sits idle for periods of time.
Good Luck