Boat is an 18' Voyager pontoon boat with a 40 hp Yamaha 4 stroke. I have a Yamaha 11 5/8D by 11"" pitch prop on the motor. At WOT I get only 4800 rpm. The engine starts on the first try cold or hot. Checked compression, spark plugs, timing and fuel pressure at idle and under load. All checks out fine. Boat runs very well except WOT is low. Tach is within 50 rpms of marine mechanics tach. Yamaha does not make props that go lower than 11'" pitch for my engine. I see props as low as 7" on the prop area of this website. What prop should I try now? 10, 9, 8, 7??? How bout diameter? I fear I will have a boatload of props the way things look!
