you was the engine ? the year ? the carb of the mixture screws turn the cw tighten then the ccw 1-1/2 ...the rpm engine is the 650 RPMS .... running the engine neutral of the engine temp 140-160 F then adjust the mixture screw adjusted it 1/2 rotations ..Okay I have had similar issues and it sounds like your timing/ fuel mixture are off. It sounds like your engine is immediately flooding itself on start up because it isn’t combusting the fuel in the cylinders soon enough. Have you changed fuel/air mixture screw or idle speed screw on carb at all?? Next time you are at the boat push the throttle SLOWLY all the way to the wide open throttle position with the throttle in NEUTRAL mode, then crank the engine and see if it starts up better. If so that means something is causes your fuel mixture to be too rich. You can also try just bumping the key to the start position multiple times for one second each in quick repetition to see if that makes it start.
did you idle timing ?