Re: prop
Couple of questions first. What is your WOT with the existing prop?
How long have you owned the boat and has this always been the case?
Reasons for the questions: You should be able to turn between 4800 to 5200 with that motor. Anything less and you're straining it, anything more and you might see parts fly off. Critical to keep those paramaters as close as possible.
If this is a new boat to you and the symptoms have always been this way then there just might be other areas that need attention.
How do you regain this lost power? For most boat owners, you don?t. The most effective way to regain the lost power is to install a supercharger or turbocharger. While possible, this isn?t practical for most boat owners. (Note: As horsepower goes down, rpm goes down, too and changing to a lower pitch prop to get the engine speed back into its recommended range will help.
As we go up in elevation, air density becomes less and those engines fitted with carburetors will begin to run rich. For prolonged operation at higher elevations (generally for two or more weeks at an elevation of 4000 feet or more) carbureted engines can be improved by installing smaller main jets to get the fuel/air ratio back to where it belongs.
