Yanmar 3YM30 engine issues

[mikequig]

I'm still betting on the easy fix: bad voltage regulator - therefore, bad alternator. With solar power disconnected and shore power disconnected, take a voltage reading across the battery bank with engine running. If voltage reading is higher than 14.5 volts....its the voltage regulator which is bad. It's an integral part of the alternator so the only fix is to replace alternator. If it's bad intermittently, and off and on calling for higher voltage output that would explain the change in rpm as the engine loads and unloads to keep the alternator spinning at whatever speed is needed to put out the voltage called for by the faulty regulator.