Marquis Gold 5500 tune-up

[unclescratch]

My generator is 18 years and 741.4 hours old. I acquired it w/motorhome this past summer and listened as the machine surged slightly while running. Time for some attention! The access hole on the very bottom for the hex head fixture for turning the crankshaft was a nice feature. I found all 4 valves slightly loose but in performing the adjustment found it somewhat challenging to hold the adjusting nut before tightening it. What size is that adjusting nut?? Not 1/2, 9/16, 13mm, 14mm.....British Whitworth??? Onan says to clean/replace the cylinder head. This I did not address. Maybe I can run the engine at speed and introduce some water from a spray bottle into the carburetor to clean the combustion chambers. But I would advise pulling the spark plugs after this in case a chunk of carbon comes loose and fouls a plug. I passed on this procedure, maybe someone has and will add what they learned from it. The spark plugs, NGK BPR 4EY, appeared to be original. I cleaned, filed, gapped (.025) and re-installed them w/a small dab of Anti seize lubricant on the first of the long threads. I pulled the float bowl and cleaned the bowl and brass parts that were part of what holds the bowl on, as well as the altitude adjusting screw and its port with an aerosol carb cleaner. I discarded the redundant fuel filter at the carb and replaced the (only slightly restricted) filter (Wix 33049) at the pump. New air filter (NAPA Gold 9087) installed after cleaning the housing and checking to find the rubber elbow at the top of the housing to be a little stiff but judged still serviceable at this time. Oil is clean and not due for service until spring. Used a small, stiff paint brush to scrub the accumulated oil residue from the exposed engine cases and oil pan before cleaning the nice heavy cover and snapping in on for the finish. I have not pulled the plug from the exhaust system to clean carbon (from the muffler?). Again, if someone has performed this, perhaps they will join in. Onan runs fine, I have some added peace of mind and confidence going forward.

[DavidM]

Great job. The only thing I would have done slightly differently is pull the carb, disassemble it and soak the parts overnight in carburetor cleaner. That process has restored every carburetor I have tried it on- 5-6 so far.

David

[Sun88]

Originally Posted by DavidM

Great job. The only thing I would have done slightly differently is pull the carb, disassemble it and soak the parts overnight in carburetor cleaner. That process has restored every carburetor I have tried it on- 5-6 so far.

David

X2 on the above, with an alternative. I too had some surging on my 5500, but I soaked the carb parts in SeaFoam overnight. Blew everything out with compressed air next day and all surging gone. I'm sure carb cleaner as described above also works. But overnight soaking and subsequent compressed air is the key - there are air passages the size of 2 human hairs in those carbs!