Last season I bought a 1978 Mariner 40 hp outboard.I took it to a mechanic to look it over.He said that it had good compresion, but that the plugs where wet. He put a head gasket on it for me. I've had to do a few things to it, but it runs good. It starts first crank every time. Soon, it had trouble getting up to speed. Once it "cleared-out", it take right off again. I pulled the plugs and they were wet. I took it back to the mechanic and he said that the head gasket was leaking again. He fixed it and I ran it a couple of times before I put it away last season. Today I was running near full speed when it suddenly began sounding differently, and then began loosing RPM's.When I slowed down, it began to smoke. I shut it down and removed the cover. The motor was hot. After it cooled, I started it up. It seemed alright, but occasionaly, would have trouble taking off or idle kinda' rough. I noticed water spray on the intake manifold. I couldn't see where it was coming from while it was idling. I would dry it, and it would be back again after running it. When I got home, I pulled the plugs; the bottom one was wet. This is the first time that it has ever got hot. There was alot of trash on the water. I'm sure it got plugged. I've got an origenal service manuel with the torque values and sequence, and I retorqued it this spring. The mechanic put the head on a plate. Why do you think the gasket keeps going out? Do you know where the water under the cowl is coming from?
