I bought a 76? Tri-hull with a 115HP Inline-6 outboard. The engine had been rebuilt but the boat had been stored for about 10 years. After cleaning entire fuel system and running the boat it would act as if it is losing power after about a minute at WOT (wide open throttle). The fuel ball was hard and so it wasn?t a fuel pick-up problem. I took it to a local boat mechanic and explained my symptoms. He pulled the plugs and the top 2 spark plugs had aluminum specks on them. He said this is due to over heating, and probably a result of a bad water pump impeller, most likely caused by the motor being started out of water. I replaced the water pump impeller but unfortunately had the same result. I then pulled the power head apart and sure enough the top two pistons were melting down. I had the block checked out by a local machine shop and he verified that the engine had been rebuilt as I was told. The block checked out good so I deglazed the cylinders and cleaned the power head, and installed two new pistons in the top two holes. A fun winter project I might add! After reinstalling the power head and mixing a fresh tank of gas 25:1 as per the good book. I took the boat to the water for some break-in time. After warming the engine up and cruising around for a few minutes, I brought the heavy old boat up to about ? throttle, and after about a minute or two, it started losing power again. I checked and adjusted my cables to insure full throttle, yet time after time I had the same results. Fearing the worst, I pulled the top spark plug. It was clean, no signs of aluminum. I then pulled the 2nd plug and it had aluminum specks on it. If I waited about 10 minutes, the engine would take rite off and accelerate up to WOT, for about 1 minute and then lose power again. Or if I was impatient, I would dump a little straight 2-stroke oil in the hole and off we would go again. For about 1 minute. I don?t want to write a book here, but does anyone have any ideas of what the problem could be that?s causing the #2 piston to heat up or seize in the cylinder. Could it be a timing issue or carburetion, and if so the later, then why no problems with the first cylinder, it shares the same carburetor?
