Buddy of mine has an Alumaweld with motor issues that has me stumped. 2001 Yamaha 50 HP 4 stroke (carbs) with approx 230 hrs on it. Motor won't rev past 4200 99% of the time and misfires like crazy when it's running at that RPM. Idle is smooth with no miss or anything. Occasionally will run up to 5400 or so but as soon as you come off step and try to go again it just stops at 4200 and starts misfiring. We've replaced the plugs and all filters (gas and fuel/water). All I can think is that he has old gas with a bunch of water in it. Added HEET and Seafoam but it doesn't seem to make a difference. Anybody got any ideas? I think he needs to drain the tank entirely but figured I'd pick the collective brains of folks here for something else that may be causing it.