I have twin Yamaha 225 4 strokes, 2004? model, new in 2005, 150 hours. One engine does 5500 RPM, and the other max's out at 5000 RPM. I have changed the plugs, run power tune thru the engine, added chevron fuel injector cleaner to the fuel, checked the butterfly valves for full opening at full throttle, checked the cross over joint connectors on the intake silencers, read the yamaha service manual. I have not checked the individual fuel injectors, or the pressure on the fuel pump. Any suggestions or comments are appreciated!