I have been working on an old jon boat for a while now. Had it on the water for the first time today. It will idle fine, but at full throttle it is only running about 30% of the rpm it should (guessing). Engine runs smooth, and doesn't smoke, just will not turn up to rpm. Linkage is good and it will rev up at idle. Just no power under load. Any ideas? I'm thinking I may have a stopped up 'jet' in the carb. Its a 1975 25hp Johnson.