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This is the exact same issue I am having. I don't have the answer but here is what I have eliminated using Yamaha diagonstic software and the service manual.@HELP maiden voyage today and the starboard engine won't get over 6500 rpm while the port gets over 8000. Anyone?
Also, I forgot to mention the very first thing that I did was to change the spark plugs, but to no effect.This is the exact same issue I am having. I don't have the answer but here is what I have eliminated using Yamaha diagonstic software and the service manual.
1. No current logged errors in ECU showing issues. (timing and or sensor failure)
2. Throttle mechanism and throttle body are currently in spec with service manual test
3. Manifold temp & pressure sensor works fine
4. Swapped ECU with starboard engine and no change
5. Without loading the engine and jet can perform just as the starboard engine
6. Plugs are black from rich mixture, which is why I believe it is limited in RPM under loading
7. I have confirmed and eliminated any air intake issues
I only have a few other items left to check.
1. Fuel pressure check, but I believe that is is not overpressuring the rail
2. Swap the cam sensor to see if that could cause a slight timing issue
3. Exhaust temp switch, could that cause an issue with fuel mixture?
4. If the timing chain is off by one(1) tooth would it throw an error in the ECU?