Re: Engine Speed
Is cav plate buried @ WOT, or can you see it clearly w/o water on top? If it's covered up, start raising the motor a hole at a time until the cav plate is uncovered and the motor doesn't cavitate in turns @ WOT. You should pickup both speed and RPM's if the motor needs to be raised. Once you get the motor setup right, then experiment with props to get 5800 RPM.
BTW that's a light boat and a big motor. When you get it right, it should be in the 45 to 50 MPH area. My '85 140 HP Johnson moved a 19' Sea Ray over 40 NMPH.