ENGINE ON BOAT (4.3L) WANTS TO KEEP RUNNING WHEN I TURN IF OFF

[CUDA8U]

 If I shut it off and try to start it right away it won't start with just a bump of the keep,do I need to adjust the carb or timing?It kind of chugs a few times before it shuts off.

4.3l gm inboard,low hrs

[69bcuda]

Some good VP and Merc knowledge here....
http://www.marineengine.com/boat-forum/forumdisplay.php?961-Gas-Inboard-Engines-Inboard-Outboards-and-Sterndrive-Forum