I have an ONAN MAJB Generator that will run for a while say, 20 min and then start going down in Rpms and either die or resume normal RPM. Mostly it will just die. I checked the water pump and it is fine. Anyone have any ideas, i have ordered a new spark plug. If i need to pull it out to work on it, do i have to pull one of the main engines to do that. I just rebuilt my port engine and will be doing the starboard next. But i would like to pull the gen set and get it working for the rest of the season.