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Old 06-15-2009, 10:35 AM   #1
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Onan smokes under load

I have a 1977 Onan BF model 4kw gas generator which I have been fixing up. I finally got it running smooth. When I hook up a light electrical load, it runs ok. When a bigger load is applie, the engine seems to bog down and smoke come out the tail pipe. The smoke is a light color (not black). I have the service manual but this problem is not directly addressed in it. Has anyone seen this exact problem before and know what the problem is?
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Old 06-15-2009, 10:40 AM   #2
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I have a 1977 Onan BF model 4kw gas generator which I have been fixing up. I finally got it running smooth. When I hook up a light electrical load, it runs ok. When a bigger load is applie, the engine seems to bog down and smoke come out the tail pipe. The smoke is a light color (not black). I have the service manual but this problem is not directly addressed in it. Has anyone seen this exact problem before and know what the problem is?

By bogging down do you mean you lose rpm? How does the voltage and frequency look? light in color? Do you mean Blue? that would be oil.
Black too much fuel. air cooled or liquid? White color would be coolant.
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Old 06-15-2009, 10:55 AM   #3
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Anything electrical, or internal combustion has smoke inside.

If the smoke comes out, they need attention, or will usually stop operating.

Never let the smoke out.
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Old 06-15-2009, 11:10 AM   #4
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1977 - It's my guess that the thing is just flat worn out and not worth the cost of repair. A very dirty air intake might be responsible but it sounds like you have addressed that sort of problem.
Cummings owns Onan and for around $50? a Cummings/Onana dealer could troubleshoot it for you. I would not use a RV dealership.
Consider replacing it with a new unit. Night and day improvement
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Old 06-15-2009, 11:11 AM   #5
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Anything electrical, or internal combustion has smoke inside.

If the smoke comes out, they need attention, or will usually stop operating.

Never let the smoke out.
I like it
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Old 06-15-2009, 02:44 PM   #6
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Never let the smoke out.[/quote]

What is it's due to coughing?
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Old 06-15-2009, 04:33 PM   #7
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I worked on tugboats for years and we always "exercised" the gen set once a week. I still do with Bess. The smoke is prolly piston rings staying in the jugs in the same position for too long.
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Old 06-15-2009, 11:15 PM   #8
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I worked on tugboats for years and we always "exercised" the gen set once a week. I still do with Bess. The smoke is prolly piston rings staying in the jugs in the same position for too long.
I had a problem not unlike that when I started a generator that had been in storage for three years. I filled the cylinder with oil when I stored it. all the oil was gone. I got it started and ran it hard for a couple of hours. the smoke stopped.
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Old 06-16-2009, 12:24 AM   #9
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Tune-up and decarbonize.

Quote:
Originally Posted by Dr.Theopolis View Post
I have a 1977 Onan BF model 4kw gas generator which I have been fixing up. I finally got it running smooth. When I hook up a light electrical load, it runs ok. When a bigger load is applie, the engine seems to bog down and smoke come out the tail pipe. The smoke is a light color (not black). I have the service manual but this problem is not directly addressed in it. Has anyone seen this exact problem before and know what the problem is?
Hi, check the air filter, adjust the carburetor, replace the spark plugs, and/or remove the heads to remove carbon build-up. Your owner's manual will tell you how to do this, or take it to an Onan dealer as previously stated, not an RV dealer.
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Old 08-02-2009, 06:01 AM   #10
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Quote:
Originally Posted by Dr.Theopolis View Post
I have a 1977 Onan BF model 4kw gas generator which I have been fixing up. I finally got it running smooth. When I hook up a light electrical load, it runs ok. When a bigger load is applie, the engine seems to bog down and smoke come out the tail pipe. The smoke is a light color (not black). I have the service manual but this problem is not directly addressed in it. Has anyone seen this exact problem before and know what the problem is?

So - - - What was the fix? Shoot it with a 44 and install a Honda?
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Old 08-02-2009, 09:45 AM   #11
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I missed this thread the first time around... If it turns out the smoke was oil, an interim fix is to drain the dino oil and put Mobil 1 in it. It will still use oil, but will no longer smoke. Even at $6 a quart, it will take a long time to equal the cost of a new generator.
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Old 08-09-2009, 11:15 AM   #12
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The fix was - sell it and buy a Honda

And I did! I finally had to get rid of it quick so I sold it for $150.

I now have a Honda eu2000ia and it is a challenge to make sure all my loads stay under 1600w but it is not impossible. I live on a boat and am very used to shutting X off so I can run Y.

With such a low power genny, I needed a lower power (and new/working) rooftop air conditioner - so I got an 8000btu which apparently has a nice starting circuit designed into it because it starts on the Honda very easily...even with the eco throttle turned on! I also replaced the perfectly working 65A Univolt with a 30A Intelli-power converter. Yes, the univolt is for sale in case there is a museum that wants it.
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