I have a 1984 Johnson 115 outboard. The boat excelerates very slowly and does not have the speed it once had (I'd say 5 to 7 mph slower). Any clues what may be causing it?
After you check compression: It may not be firing on all 4 cyls. Water in the fuel. Restriction in the carb fuel passages. Weak fuel pump. It's either a fuel or spark issue. Easy/simple to check spark first.
After compression test, I would check for a waterlogged boat. If the boat is moored,or left uncovered, and has a floor, the foam may be full of water. Its something I find up here where boats seem to last for ever.