TOPIC: Johnson won’t run in water

71 Johnson 85hp. Runs great dry, starts no problem. If motor is lowered into water the engine barely turns over if at all. It seems to lock up. I did compression test, all 4 cylinders are only a few psi apart around 120 psi. Leak down test showed very good seal. What could be wrong??? Could water be getting into crankcase? If so, what would possibly be the culprit? I was thinking bad head gasket(s), but top end and rings seem fine. Thanks in advance for any help.

Let's think this through. If it runs good on land, has good compression etc. then you know it's not the motor itself. When you say "lowered into water" how deep are you putting it? When you run it on dry land do you use muffs or are you lowering it in a tank?
The first thing to check is your wiring at the motor end. Make sure all the contacts are clean and dry. The two main wires from the battery to the starter motor should be solid, the black wire from the battery to the engine block should be tight and clean. Make sure the connections/plug are clean and dry. A bad or corroded wire/connection will make for hard starting and slow cranking.

Check your exhaust relief ports for blockage