Thank you for helping me with my question.
I have recently bought a 1979 Evinrude 15 hp project motor for a hydroplane I built this winter. The motor needed some repairs and over the winter I replaced the fuel lines, replaced the low idle adjustment screw knob, rebuilt the recoil starter, replaced the high-speed anti-starting paul and replaced the water pump. Compression seems good and the engine starts and runs.
I recently took the engine out for a test drive on a 12-foot MirroCraft. The engine and drive run well until about half throttle. It then loses power and the engine starts to over rev.
Is there a re-assembly adjustment I need to make to the drive shaft or lower unit drive gears following the removal of the lower unit for the water pump repair?
What else may be causing the engine to lose drive power? I have a hard time believing this is cavitation. I will be taking the engine out for another spin to take it through full trim adjustments. The drive shaft splines looked good at both ends when I had it out.
Normally it will work fine at lower speed and then start spinning as you put more power to it. To check it you can pull the prop and mark a line from the outside through the middle to the other side. Take it for a run and then see if the marks are in or out of line. I have a new to me 1979 9.9 that I completely worked over this winter. Took it out on Sunday and it ran like a dog. Perfect it the barrel and then very disappointing on the boat. Oh well, something more to do. Best of luck. Rick.
I took the prop off and found rubber bits all around the drive splines. It appears the rubber joint holding the bronze drive coupling to the aluminum prop casting has reached end of life.
Thank you, again.