QUOTE(jazzman1009 @ Oct 12 2012, 07:58 PM)
Hi all, I need some advice on a generator issue. I have an Onan Marquis Gold 5.5. It is having trouble running properly when placed under a load (AC, Water Heater, etc.). The problem never existed until recently. When placing a load on it, it would start to act like it wants to stall, RPM's go down, sputters, backfires, then seems to recover. After a couple of minutes, or sometimes sooner, it will do it again. Seems to clear up after it is running for awhile and is hot. Then another problem popped up with the thing not starting at all. I ended up replacing the carb and it starts right up, but the original running under a load problem is back. It was then suggested I was having a fuel pump problem, replaced that today to no avail. Has anyone experienced a similar problem with this model generator? I hate to keep throwing money at it and not having the problem solved. I am wondering if I just don't have a set of bad plugs? Again, it appears the problem goes away if it has run for quite sometime with no load. Any suggestions are appreciated!
It sounds like your genset is having breathing problems. Have you used Onan Carburator cleaner per owner's manual. More important than cleaning the carburator, the cleaner removes carbon deposits from the combustion chamber. Just replacing the carburator will not help the combustion chamber breathe easier. Also check to see if your unit has a plug in the muffeler with which to purge accumulated carbon from the spark arrestor, which also can also plug up your system. Remove plug, run genset under full load, (AC[s], microwave etc.. as much as the genset will handle), for about 15 minutes, wait for muffeler to cool off, and reinsert the plug. If your genset is approaching 500 hrs, it is getting time for a major tuneup, where the techs will, among other things, remove the heads and manually scrape the carbon deposits out.