I am currently working on a 1987 70HP Mercury motor. The previous owner said it started to smoke and run rough, so he shut it off. Ever since then, the starter would just click. I looked over the motor and a fuel line for the center cylinder was broken. I repaired that and moved to the clicking sound. The motor turned over easily with a breaker bar and socket. I took out the battery and had it checked. It failed and was replaced. Tried to start again, and it clicked. So I put in a new starter and checked all the wires, and replaced the solenoid just to get a new starting point. I hit the key with the new starter and the motor spun like normal. So thinking all was ok, I hooked up the hose to the water pump and tried to start it. It spun fast then slowed down to the point where the starter will just turn the flywheel 1/4 revolution. Fearing the worst, I tried the turn the motor over with a breaker bar. The more I try to turn it over clockwise (engine rotation) the tighter it gets. If I go opposite the engine rotation, it spins easily. I don't have a lot of experience with outboards, but this one has me stumped. The engine does not turn over easier if the plugs are out, either. It almost seems to me there is some sort of issue with hydro lock, and this is where I am stumped.
