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Old 09-19-2021, 01:53 PM   #1
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Onan 4000 generator issues

Hey everyone,


So I am having what seems like a somewhat common issue per my searching the internet and this forum. I have a Onan 4ky spec S generator and it willl start up but only run about 6-8 minutes and shut off and wont restart. It gives me the 36 error, which just means unexpected shut off. It will not start again until the next day or perhaps when it has completely cooled down. Here is what i have done so far...


1. Gas level in coach is FULL (so no need to tell me about the 1/4 tank shut off, lol)
2. Replaced the fuel filter
3. Replaced the spark plug, and confirmed it has a spark.
4. Changed the oil, and made sure it is the proper level, not overfilled.

5. Tested the fuel pump when cold (unplugged gas line at the carb and pushed start and had a solid flow of gas. Pressed Prime and had a solid flow of gas.
6. Tested the fuel pump after it shut down and wouldnt restart. Same results as when cold, solid flow of gas. Based on the fuel pump test, i am lead to believe that the fuel pump is not the problem?
7. I bought a fresh gallon of gas and dumped in Seafoam, and put a gas line from the gas can direct to the fuel filter and started lit and let it run until it died (about 5 or 6 minutes) and left it alone. Same result, nothing changed.




Do you think it is a bad/gummed up carb? I exercised the generator monthly for 30-40 minutes before this, and the unit only has about 50 hours on it if that. A new Onan carb is $395 per my call to Onan on Friday, but they are back ordered and they have no clue when they will get one back in. I can buy aftermarket ones on amazon for a fraction of the cost, but based on reviews it is hit or miss if you get one that is any count.



Unless I am wrong about the fuel pump, i feel i must be something with the carb, any ideas?


Thanks in advanced for any input!
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Old 09-19-2021, 02:16 PM   #2
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When it runs for 6~8 minutes, does it run good? No surging or missing? How about any changes, are you at a higher altitude or in a high heat area? Generally speaking, when I have dealt with a gummed up carburetor on other engines, the engine doesn't run good for even a few minutes. Also, just to check, have you checked the oil level? ~CA
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Old 09-19-2021, 02:36 PM   #3
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Quote:
Originally Posted by craigav View Post
When it runs for 6~8 minutes, does it run good? No surging or missing? How about any changes, are you at a higher altitude or in a high heat area? Generally speaking, when I have dealt with a gummed up carburetor on other engines, the engine doesn't run good for even a few minutes. Also, just to check, have you checked the oil level? ~CA
Yes it runs very good, like normal. Right before it dies I do get what seems like a surge.

Yes on oil level, I have read numerous posts ect about the oil level. I have it where it reads just above the fill line on the dip stick.

No change in altitude.
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Old 09-19-2021, 02:44 PM   #4
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I once fixed my parents Onan Marquee generator that had a gummed up carburetor by loosening the bowl drain screw, and spraying Onan 4C up into the bowl, then letting it sit for a few hours. Then I drained it, and sprayed it up in there again, and drained it again. What came out was very dirty, especially the first time.

The dealer had told me it would need a new carburetor, but I ran down there and picked up the 4C, came back and used it, and a generator ran beautifully afterwards.

I now have an Onan 4000, and it should work on that as well. Haven't had to do it yet, I try to run it pretty regularly.
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Old 09-19-2021, 03:11 PM   #5
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Originally Posted by TampaRv View Post
Yes it runs very good, like normal. Right before it dies I do get what seems like a surge.

Yes on oil level, I have read numerous posts ect about the oil level. I have it where it reads just above the fill line on the dip stick.

No change in altitude.

I would try it without any heavy load (no a/c) and see if it runs longer, if it is fuel starvation, then you should notice that it runs longer w/o a load compared to being under a load. Keep in mind that it is not a great idea to have the a/c on when shutting down the generator... or when it shuts itself down (many people do it though w/o problems, just that there is a chance for a surge in electricity). ~CA
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Old 09-20-2021, 12:28 AM   #6
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Manually priming the generator before starting would fill the carburetor bowl. I'd think the bowl would run out of fuel in less than 5 or 6 minutes but,,, is it possible the fuel pump isn't getting power while the genset is operating? Bad electronic board maybe?
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