I’ve got a John Deere 325 skid steer, it runs smooth as it should but intermittently will rev up them immediately go back to running right. It isn’t a fuel delivery problem, I’m thinking something with the governor? Has anybody dealt with this?
Usually when engine rpm's do that it is an indication of air ingestion. I would put a clear line in the fuel return line and make a vertical loop with the line and the watch to see if there is air in the fuel while the engine is running.