I have a 1963 Thompson I am restoring. It came with a 62 Johnson 72 that
runs. After two years, I had it in the water.
When the boat is on land and I have the motor in the "bucket" I can see no
difficulty. But when I took it out on the water, the engine ran fine with
one problem. The access hatch to the carbs had to be open, the boat would
run as if it just was out of time every now and them, but if I shut the
access door, the engine would just lug down and start to quit open the
access door and it would run pretty much ok. I have checked the air intake
opening and filter on the underside and it is fine.

Any suggestions?