burning rich, very rich. Float not set properly and idle/mixture not set properly. Don't waste your time on a compression check.
Be VERY careful with "the boat smells like gas" as vapors/fumes can cause problems.
Get it fixed, properly or do it yourself. At this point you would be better off ordering a new carb and replacing it yourself, than to give this person more money to "repair" what he has already broken. No more money for him, till it idles smoothly. He is not a mechanic.
While you may have a valve or piston problem, that is secondary to the carb getting repaired.
I also loaned him my 2HP Honda 4 stroke, same result. Even after I cleaned the carb twice, I could never get it to run spot on. A $100 new Honda carb did the trick.