I would agree with this. We used to service Onan generators and this was a fairly common problem. The exhaust is raw water cooled at the exhaust elbow and they corrode after 4-5 years of service. If you dropped 3" of pitch and the rpm's still didn't pick up your engine is not making power. I wasted about 40 hours rebuilding an onan, chasing the fuel system, timing etc to learn this one.