Re: 2002 yamaha 90 2 stroke funny thing
First -- what prop pitch do you have now. Second -- Stop reving the engine to 6000 RPM in neutral or you may find yourself not being able to turn it off as it enters "runaway" mode and it self destructs. An engine running on half its cylinders will rev very high because there is no load on it. It revs higher in reverse because a prop cannot be as efficient running backward as it is forward. Studying the shape of the blades should explain why. Third -- what speed were you going at 2900 RPM?
I don't see any way just the prop being the problem. That motor with the proper prop should run 5500. To gain 2600 rpm you would need to change pitch by approximately 13 inches and that is simply unreasonable unless the prop you have now is a 26P which is also unreasonable on that engine. That combination should have a a 13-1/4x13P prop (about) and for your Yammy that part number is 6E5-45949-00-EL. Before you launch into a new prop, make sure the tach is accurate. I would also make sure the engine is running properly and that there is no water in the tubes.
