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Old 09-19-2012, 10:02 AM   #1
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Onan Generator, maintaining and running a 4000 watt

Hi Everyone, I own a 23ft 1988 class A RV with a Onan 4kw 4BGE genny.

I have tried to learn as much as I can about it and try to keep it running properly. I have added a double/triple dose of Seafoam to the RV tank and run it a few times a day for a week. It helps but there are a few questions.

It runs but sounds weird and I am trying to adjust it. It puts out @115-118v and varies between 60.1- 62 hz between no load and 1/2 - 3/4 load.

I've managed to get it all running OK, yet the manual says that the main jet should be @ 1-1/4 turns yet mine is @2-1/2 turns, and the idle jet should be @ 1 turn yet I have @2-1/4 turns.

It generally doesn't surge anymore (the Seafoam helped) but it sounds like it is running on one cylinder or not extremely smooth. Definitely not quiet nor smooth running like a Kipor 2000w portable that I have at home.

How do you folks maintain or adjust your gennies?

PS: I have changed the oil, and I managed to changed the air filter, yet I can't access the rear plug, points etc... There is @ 1/2" clearance all the way around. I don't have a drawer so it looks like quite a job to remove the generator :(

Any older generator owners here?
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Old 09-19-2012, 10:42 AM   #2
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Sounds to me like you have alot of varnish in carb. The treatment will help a little,but the carb. will have to be taken off and cleaned.Looking at picture it don't look like it will be hard to remove carb. Remove carb and get some spray carb cleaner(walmart sells it or any parts store) take bowl off bottom & remove float & needle,then remove jets from carb.,remove adj. screw then take cleaner & spray all holes until you see it coming from inside of carb. throat behind the butterfly. If it dosent come out holes get a small piece of wire & run through hole,after cleaning everything put back together & run adj. screw all the way in & then out about one & a half turns.Let gen. get warm before trying to adj. carb any more. Hope this helps
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Old 09-19-2012, 11:24 AM   #3
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I bought one just like yours that is installed in my RV. It ran when I bought it, but pretty much like yours is running. It was running really rich, missing, and surging. The previous owner said he had "Cleaned the Carb"..

Well, I took the carb off.. Pulled the fuel bowl and found the low speed jet completely plugged. It has been a few years ago since I did it, didn't take pictures inside the carb. It is located in a passage pretty much beside the main jet passage. It was so plugged up it looked like it had a rubber plug in the hole. Was just gunk...
With the low speed jet (Pilot Jet in my motorcycle world) plugged the engine starves for fuel, the governor adjusts the throttle to bring the RPM back up, that gets it into the main jet, engine goes too fast, governor slows it down, runs out of fuel again, repeat process, get surge...
Anyway, once that jet was clean I could get the engine to slow down where it should, no surge, get the voltage and frequency right, and it ran clean on both cylinders...

Carb removed.


Used a Killowatt to measure voltage and frequency. The toaster oven and blow dryer were loads. Worked great..
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Old 09-19-2012, 11:28 AM   #4
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Quote:
Originally Posted by Tim Mitchell View Post
Sounds to me like you have alot of varnish in carb. The treatment will help a little,but the carb. will have to be taken off and cleaned.Looking at picture it don't look like it will be hard to remove carb. Remove carb and get some spray carb cleaner(walmart sells it or any parts store) take bowl off bottom & remove float & needle,then remove jets from carb.,remove adj. screw then take cleaner & spray all holes until you see it coming from inside of carb. throat behind the butterfly. If it dosent come out holes get a small piece of wire & run through hole,after cleaning everything put back together & run adj. screw all the way in & then out about one & a half turns.Let gen. get warm before trying to adj. carb any more. Hope this helps
Hi Tim, since I am not really equipped to remove and clean the carb, would a B-12 cleaner remove the varnish better than Seafoam. I could give it a double/triple dose over a weeks period to clean it?

Does taking the carb off require a carb kit (gaskets, jets etc..) and does it require fiddling with the choke?

If I don't take the carb off and can try to adjust the main and idle jets to run good, would I still have to clean the varnish out?

If I manage to play with the idle & main jet and get the genny to run fairly well without puffing black smoke (rich) or surging (lean), will any thing be damaged if I don't take off the carb and clean it?

Naturally it means adjusting/running the genny within voltage and hertz specifications.

Thanks for all your help, IAN...
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Old 09-19-2012, 11:48 AM   #5
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Originally Posted by Sprdtyf350 View Post
I bought one just like yours that is installed in my RV. It ran when I bought it, but pretty much like yours is running. It was running really rich, missing, and surging. The previous owner said he had "Cleaned the Carb"..

Well, I took the carb off.. Pulled the fuel bowl and found the low speed jet completely plugged. It has been a few years ago since I did it, didn't take pictures inside the carb. It is located in a passage pretty much beside the main jet passage. It was so plugged up it looked like it had a rubber plug in the hole. Was just gunk...
With the low speed jet (Pilot Jet in my motorcycle world) plugged the engine starves for fuel, the governor adjusts the throttle to bring the RPM back up, that gets it into the main jet, engine goes too fast, governor slows it down, runs out of fuel again, repeat process, get surge...
Anyway, once that jet was clean I could get the engine to slow down where it should, no surge, get the voltage and frequency right, and it ran clean on both cylinders...
Hi Sprdtyf350, I see we have the same unit, the only difference is mine doesn't slide out which makes EVERYTHING a nightmare to do anything. It actually took me an hour just to get the bolt out that holds the air cleaner :(

In reality the genny produces good voltage and hertz, but it doesn't seem to be running very smooth. There always seems to have a shake going on.

I thought it was a little strange that my carb screw adjustments were double what the service manual calls for. I can tell if it is running rich or lean. I do get a puff of black smoke when it starts from an overnight of being off.

When I look at the exhaust after it has warmed up I don't really see any white or black smoke. The front spark plug electrode was grey/light tan when I checked it last week.

To better explain, maybe I can post a small video of how it runs and sounds?
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Old 09-19-2012, 11:55 AM   #6
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You pretty much need to gain access to the other other plug, points, and carb.. throwing chemicals at it now will not do much. I know its a pain, mines the same way..
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Old 09-19-2012, 12:14 PM   #7
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You have access from the bottom right? It's just 4 bolts, a fuel line, and a couple electrical connections holding it in. Maybe if you remove the mount bolts, you can slide it out 5-6 inches to help with access. Just don't let it fall on your toes.. Heavy

If your carb is gunked up like mine was you can pour/spray all the chemicals you want and never get it to run right. The point gap is also an important setting to check also.. It is what sets your timing..

Me... I would remove it. If your like me talking yourself into getting started is the hardest part.. After that it's just bolts...
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Old 09-19-2012, 12:22 PM   #8
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4 Bolts

I had one of these in a 1992 Honey motorhome. Even when new it was a cantankerous thing and required constant attention.

Looking at the picture it looks like you should be able to slide the genset out by removing the 4 mounting bolts on the bottom plate. If I remember right they are carriage bolts and easy to remove.

Once you slide it out everything else is easy.

It probably needs more than just a carb cleaning. Hope you can still find points for it. If you can find an electronic module to replace the points I would highly recommend doing so.

FYI: I found the points on eBay for $15, and a carb repair kit for $10. eBay could be your new best friend.
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Old 09-19-2012, 12:33 PM   #9
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You pretty much need to gain access to the other other plug, points, and carb.. throwing chemicals at it now will not do much. I know its a pain, mines the same way..
Hi Midniteoyl, access on these is a nightmare. If soaking in carb cleaner will clean it, why doesn't running some through the fuel help clean it out, especially since I can do a double/triple dose and let it sit overnight for a period of a week?
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Old 09-19-2012, 12:36 PM   #10
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Originally Posted by Sprdtyf350 View Post
You have access from the bottom right? It's just 4 bolts, a fuel line, and a couple electrical connections holding it in. Maybe if you remove the mount bolts, you can slide it out 5-6 inches to help with access. Just don't let it fall on your toes.. Heavy

If your carb is gunked up like mine was you can pour/spray all the chemicals you want and never get it to run right. The point gap is also an important setting to check also.. It is what sets your timing..

Me... I would remove it. If your like me talking yourself into getting started is the hardest part.. After that it's just bolts...
From the little that I can see there's two bolts holding the frame in. I guess I have to drop the exhaust/muffler to slide it out. Disconnect the red battery cable, the fuel line, and hopefully the 120v AC cable can stay intact.

Maybe than I can slide it out @12" to rest it on a milk crate or something that handles 200 lbs. Wow, what a job this is turning out to be.. :(
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Old 09-19-2012, 12:38 PM   #11
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Originally Posted by Muddypaws View Post
I had one of these in a 1992 Honey motorhome. Even when new it was a cantankerous thing and required constant attention.

Looking at the picture it looks like you should be able to slide the genset out by removing the 4 mounting bolts on the bottom plate. If I remember right they are carriage bolts and easy to remove.

Once you slide it out everything else is easy.

It probably needs more than just a carb cleaning. Hope you can still find points for it. If you can find an electronic module to replace the points I would highly recommend doing so.

FYI: I found the points on eBay for $15, and a carb repair kit for $10. eBay could be your new best friend.

I have a new set of points, but I wasn't aware that removing the carb to clean would require a "carb kit"?

I thought I could let it soak in some cleaner than pass a fine wire thru the small jets?
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Old 09-19-2012, 12:55 PM   #12
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I didn't need a carb kit. I also didn't need new points. Or plugs.. How many hours are on your unit?

There should be 4 bolts. Basically one in each corner of the tray the generator mounts to. I can see the front 2 in your picture. I suppose it is possible your mount could have a lip of sorts that the generator slides into at the back. Maybe remove the front 2 bolts and see if it moves. If not, then there's 2 more.

Fuel line, battery connector, remote starter connector are all right there in the right front. The electrical line may be able to stay connected if they made it long enough.

Do you have a manual for the generator? If not, here is a link to it.
http://www.cumminsonan.com/www/pdf/manuals/965-0530.pdf
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Old 09-19-2012, 01:07 PM   #13
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I didn't need a carb kit. I also didn't need new points. Or plugs.. How many hours are on your unit?

There should be 4 bolts. Basically one in each corner of the tray the generator mounts to. I can see the front 2 in your picture. I suppose it is possible your mount could have a lip of sorts that the generator slides into at the back. Maybe remove the front 2 bolts and see if it moves. If not, then there's 2 more.

Fuel line, battery connector, remote starter connector are all right there in the right front. The electrical line may be able to stay connected if they made it long enough.

Do you have a manual for the generator? If not, here is a link to it.
http://www.cumminsonan.com/www/pdf/manuals/965-0530.pdf
So the carb can be soaked, cleaned, and re-assembled without a "carb kit"?

My unit has 150 hrs on it, and it's a 1988. The previous owner apparently had it serviced at Onan before I bought the unit, but I don't remember what he had done.

I can see only 2 front hex bolts holding the front of the Onan, so I imagine the frame would slide out if I disconnect everything.

I haven't been able to locate a fuel filter, so I don't know if I am supposed to have one?

Thanks for the manual, that will help a lot
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Old 09-19-2012, 01:17 PM   #14
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Take a look at pages 6-11 to 6-15. If you haven't done those you might want to. You may be able to get it running right by just getting the carb and governor adjusted correctly. There are adjustments for with load, without a load, frequency, voltage.. These are the adjustments I used the Killowatt, toaster, and blow dryer. High tech I know... But they worked great for the job.

There isn't a whole lot inside the carb that can wear out. The bowl gasket is about it. Fuel needle and seat sometimes but mine were fine. The rest just gets dirty.

150 hours is hardly anything. So I would not really be super concerned with everything being worn out.

I installed a filter in the fuel line. You can see it in my picture not far from where the line hooks to the fuel pump.
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