Bought A 1976 Merc 650 at auction. Replaced the impeller,replaced lower unit grease and put it on our boat. Starts ok and shifts fine. When I give it throttle it doesn't immediately hit full power. If I run it for several minutes it seems to "kick in" and then runs smooth and I can go 30mph. I admit I did not put in new plugs yet (but will). Could this be the problem? Also will "Seafoam" the gas. Any other suggestions? Thanks.
