7.5 hp Merc high speed problem

[jmccartney@indy.rr.com]

I have a 1982? (s/n 5816301) 7.5 hp Merc that went swimming last summer. It was running went it went in and spent about 5 minutes underwater. We pulled it out and got it running right away. At about 3/4 throttle it starts to sputter and will not come up to speed. Plugs have been changed, a different carb was tried and still the same problem. It starts fine and runs good until about 3/4 throttle. When I leave it at 1/2 throttle and manually open the carb butterfly(?) it seams to want to run. It may be in the spark advance? Anyways, any suggestions on fixing this would be of great help.