I have a Honda EMS 4000 Generator. It started to run rough lately. I cleaned and rebuilt the carb with a new needle, seat and float. The spark plug fouls after about 8 hours of run time. Now it is starting to consume oil. I am adding oil every 2 hours of run time. The spark plug is still fouling - very black. A compression test show 50 psi. Does the engine need rebuilding or are there other options? How hard are these engines to rebuild? Thanks.