Robert, I know this isn't an outboard but maybe you can get me headed in the right direction. The engine is a 1987 V6 4.3L. The previous owner stated that the original problem was water got into the #4 cylinder. He had both manifolds and risers replaced with new. After the repairs, he said at full throttle, engine power would drop off considerably. His mechanic told him that either it had a stuck valve or the piston rings were bad on that cylinder. After bringing home, I got it started (briefly so as not to damage anything) and the engine idles nice and smooth. I did a compression check and the readings varied between 125# and 145#. Could this engine have mechanical problems or should I be looking at the fuel and ignition systems. Also, he had the water pump and fuel pump changed. It has a thunderbolt ignition system.