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Old 10-13-2011, 12:07 PM   #1
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Onan gen

some of you may remember my 1978 GMC Midas class A (Ole' Koot). well since he had sat for 10 yrs and the gen. gas tank had 20 galls. of varnish gas in it, I finnaly got it all out. put 10 galls of new gas in and sta-bil added. got it started and it ran fine. then it started to run fast then slow. I got a gall of gas and a can of sea foam added. put the fuel line in my gas can and ran it for 2 hrs. still doing the same thing. anyone got an idea on what I can do next. it was supposed to have had the carb cleaned but when I looked at it that carb was never taken off. they said they also put in a new fuel pump(the dealer) that may be true but I doubt it. could a smashed wire at the fuel pump cause this irregular running? any suggestions would help alot. thanks all.

Outlaw
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Old 10-13-2011, 01:39 PM   #2
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Can you provide the Onan Model number information of the ID plate. Onan made several models odf generators and it is best to know what model you have first. Coach mfg's used different models depending on options in the rig.

Dave
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Old 10-13-2011, 05:17 PM   #3
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I'd check the slip rings. Once it starts surging you will burn out the regulator quick. Here is a link to the process:

Just FYI Onan generators
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Old 10-13-2011, 08:27 PM   #4
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billieg, thanks, will take alook and see if thats a prob. will also look for what gen this is and post the #'s.

Outlaw
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Old 10-13-2011, 09:53 PM   #5
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The Marquis 5500 in my 99 pace arrow would surge like that if it didn't get used enough.

This was a gas aircooled v twin. With the cover ofrf, I could see that it had a governor linkage similar to that used on lawnmower engines, where the link on the throttle goes into a shaft in the crankcase.
Anyway, even with no load, the link was opening and closing the throttle. If I held it still, it would run at a constant speed. ditto if I turned the a/c's on to load it up.

I changed the fuel filter and spark plugs, and pulled and cleaned out the carb. Then I just let it run. I put the fridge on a/c, and the water heater, to get some load on it, and just left it run. After a day or so it smoothed out nice.

From then on, I was very careful to run it on full load (both a/c's, fridge, and water heater) for at least 30 minutes a month.
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Old 10-14-2011, 08:12 PM   #6
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yeah, I did the same thing, once the sea foam hit it started to run good, I let it run for about 20 min. then I went in and turned on everything to get a good load on it, it ran for maybe 10 min. then started back to it's high low running so I went back inside and hooked up the portable heater, smae thing then it triped the box. I turned everything off flipped the switch and started up the gen. same thing fast then slow, I held oped the lever and it would run good for a little bit then back to it's thing even while I was holding the rod, let it go same thing. I just let it run till it sucked up the gallon of gas then shut it off. hooked up back to it's tank and same thing. so ya know what I get to do next.lol. oh the owning of a vintage. ya gota luv em to own em.lol.

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Old 10-15-2011, 11:35 AM   #7
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Like I said, mine started surging on a trip all of a sudden and I tried to adjust it with the screw on top of the linkage. It sort of worked but the voltage was still going all over the place. About 3 hrs later it stopped and wouldn't start. The micanantic at Coumins said the slip rings were real dirty and that caused the voltage regulator to fry.... I wouldn't run it too long surging without checking those slip rings.
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Old 10-15-2011, 11:51 AM   #8
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Quote:
Originally Posted by Outlaw45 View Post
yeah, I did the same thing, once the sea foam hit it started to run good, I let it run for about 20 min. then I went in and turned on everything to get a good load on it, it ran for maybe 10 min. then started back to it's high low running so I went back inside and hooked up the portable heater, smae thing then it triped the box. I turned everything off flipped the switch and started up the gen. same thing fast then slow, I held oped the lever and it would run good for a little bit then back to it's thing even while I was holding the rod, let it go same thing. I just let it run till it sucked up the gallon of gas then shut it off. hooked up back to it's tank and same thing. so ya know what I get to do next.lol. oh the owning of a vintage. ya gota luv em to own em.lol.

Outlaw
Yours is a dirty jet in the carb...
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Old 10-15-2011, 08:19 PM   #9
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Jim, am cleaning the carb so will see how that works.
I can't seem to find the slip rings. I took off a cover the had vent in it and there are brushes and all the electric stuff but I didn't see a plate to clean. this is on the gen side. on the motor side there is a round cover but I can't get to that unless I unbolt the whole unit and turn it so I can get to it. just no room to get my hands back there. so where are the slip rings? thanks for all the answers so far. I did pull the 2 plugs and clean em. they were black but not oilly, found one of my plug in to loose so crimped it down to fit tight on the plug. started it up and it ran smooth. let it run for about 5 min and went inside and put a load on it and back it went to it's old stuff. shut it down and pulled the carb. will get it cleaned up and put back on so mon. we shall see. thanks.

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Old 10-15-2011, 11:43 PM   #10
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Make sure the jet is clean and screwed in tight.. I just had a gen that the jet was loose.. did the same 'surging'.
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Old 10-16-2011, 12:07 AM   #11
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Like I said in post #2, if you provide the model number of your Onan I might be able to provide you with the service manual so your not running in the dark with this.

Dave
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Old 10-16-2011, 01:34 PM   #12
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Dave, sorry. got busy with cleaning the carb. will get all the #'s for you tommorow. thank you.

Outlaw
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