I bought this 1973 Onan 5CCK 5kw 120/240 volt generator January of 2020, right before Covid hit (I also have an old, loud Generac 120/240v 5kw generator from the 90's but got on the Onan 5CCK kick in 2019). I use this Onan when the power goes out. It's not terribly fuel efficient so if I don't need to run the 240v well pump, I can get away with using my Pulsar 2kw 120-only inverter generator to run the house if I switch off all 240 volt circuit breakers and make sure the two laser printers in the office are turned off (they take a ton of wattage when they first come on).
Anyway, it's probably been two or three years since I started up the Onan 5CCK so I figured today was the day. It managed to start after several tries with the starter button and ran for a minute or so but then started missing and finally died. I don't have a recent photo of it but the below one is shortly after I first got it. I added the little grey box on the side of the switch panel, which shows volts/amps/hertz of each 120v leg.
I figured the engine issue was the carburetor, as I've never cleaned it and it's anybody's guess when it was cleaned, if ever. I studied things a little and noticed the two carb hold-down bolts come up from the bottom side of the intake manifold, and to get to them required removing the intake/exhaust system. I decided to just pull the top off the carb and clean out as much as I could.
It wasn't very dirty but I sprayed carb cleaner all over, then put the carb back together. The generator still had issues. Ok, time to bite the bullet and completely remove the carb. That meant that the gas tank had to come off, as the exhaust bracket held the tank in place. The muffler supports then had to be unbolted from the side of the generator. Then the intake/exhaust bolts were removed so the manifold and exhaust system could be finagled enough to get a box wrench onto the two carb bolts. And here I thought these old generators were easy to work on. Nope.
I didn't find anything wrong with the carburetor but I blew a bunch of carb cleaner through all the passages (again).
Back together it went. I didn't know this but it was made by Marvel Schebler, who made the majority of carburetors used on vintage tractors.
After trying and failing to get the generator going again (backfiring, cleaning the points, cleaning the spark plugs, trying different old plugs), I finally put in two "newer" spark plugs. That made the difference and the generator started right up. I don't quite understand how the generator started with the old plugs but then they somehow stopped working. That's not something that usually happens, which is why I went down the carburetor and points rabbit holes. Note to self, replace the spark plugs more often.
No-load output is 125-127 volts and 62 hertz. This generator's power output is very stable when it is running good, and it runs at 1800 RPM so it is a pretty mellow tone, unlike all the noisy new ones that run at 3600 RPM.
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