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Posted By: Florida Cracker on 03/10/04 09:40am

The 4K Onan gen. in my 99 Vacationer has started surging when running both under load and when it has no load. It continually revs up and idles back at the rate of about once every 2 or 3 seconds, power fluctuates from approx.100V to 115V. I can see the throttle linkage from the gov. moving with the surging but am not sure if the gov. is causing the problem or is being controlled by something else. When the linkage is held still the engine seems to run normally. The gen set is not run very much and really gets more use from its monthly maintenance than in normal use.
Thanks for any hints on trouble shooting or repair.


(And one spoiled rotten little dog)

Posted By: Dick Trewhella on 03/10/04 09:55am

Possibly your charger is calling, Frig is on, shut off all the circuit breakers, before you take it to onan shop. Its imbaresing if they just shut off your frig.

Happy Motoring
Dick T.
89 Coachman 27


Posted By: dirko on 03/10/04 10:41am

Hi Ho: Surging is usually a symptom of engine not being quite up to snuff (tune-up, bad gas, etc.) The governor is a feed-back servo system. If something is out of whack the loop becomes oscillatory (underdamped if you will) and it hunts. It might be time to clean the carbureator and do a tune up?

2006 Tiffin Phaeton 40QDH

Posted By: hud3ma on 03/10/04 10:43am

Sounds like it's running on a lean air-fuel mixture, which is not uncommon to engines that sit idle much of the time. They get partially clogged jets, etc. The complexity of the fix will depend on the cause of the problem.

Mike & Karen
...and Ziggy, the Golden Retriever

2002 THOR (Dutchmen) 25' Class C w/slide

Posted By: LilRedTruck on 03/10/04 10:43am

Sounds to me like the carb needs cleaning, possibly the spark plug too ! Maybe could run some carb cleaner thru it ! I think its gummed up some from sitting! Good luck ! Dan

Dan and Judy 2004 Keystone Cougar 276 EFS 2001 GMC Sierra 3500 Ext Cab Long Box 4x4 D/A Reese 16K Hitch. Jordan Ultima 2020 Brake Controller. Schefenaker Mirrors. Honda EU3000is Generator [img] height=214 width=320[/img] [img]

Note: Due to invalid formatting, all formatting has been ignored.

Posted By: Florida Cracker on 03/10/04 10:55am

Went out to try your suggestions,(I'd already tried the usual, plugs filter etc.) everything was off before but I thought I’d throw all the breakers to make sure. Low and behold it started up fine and settled in at a nice steady AC voltage both with and without a load. It was surging last week when I ran it for about an Hr. and then again today when I went out to work on it but now two Hrs. later its fine. I hate intermittent problems, now it will probably stay fixed until I’m on the road somewhere. I’m going to recheck the fuel filter etc. anyway but after that I’ll just let it run all afternoon with the electric heater turned on.
Many thanks for the help.

Posted By: Kingpin XX60 on 03/10/04 12:20pm

I spent a year trying to get Onan to fix a generator issue they said did not exist. Finally thrid time was the charm. First of all onan generators need to run 2 hrs every month at a least 1/2 load, so for 4000 wat gen that would be about 15 amps. The number one thing onan will always say is a generator has varnish in the carb for lack of use. The carbs are sealed you can't clean one it has to be replaced at around 350.00 for a new one. My 5500 generator was doing the same thing onan finally agreed to replace electronic govenor and it fixed the problem. On the way to the govenor, they replace the carb, they said it had varnish in it. I said okay lets take it apart and show me the varnish, they replace it under warranty. Then they said the enginee was all full of carbon because I wasn't running under enough load. I said DUH that's why it's hear it won't run under a load it surges and then finally shuts down. After replacing the electronic govenor it finally fixed the problem. Also repalced plugs, fuel filter but the govenor did the trick. By the way enginee rpm is set by the govenor, don't try to increase RPM via the govenor it can mess up the generator. I also own a vacationer, good luck

Posted By: mr. ed on 03/10/04 04:46pm

My Onan 6.5kw had a similar problem last year. They installed a new carb (only charged $120...I've been told they're usually more). At the same time, I had new brushes installed and the commutator cleaned. All was OK for a short while, then during a trip to Texas it started acting up worse than before. I took my coach to a Cummins repair place in San Antonio and they found that a vacuum device that operates the choke was sticking. Having sprayed some WD-40 into the unit, my genset's been working fine ever since.

Mr. Ed (fulltiming since 1987)
Life is fragile. Handle with prayer.

2007 Hitchhiker II LS Model 29.5 LKTG (sold)
2007 Dodge Ram 3500/6.7 CTD/QC/4X4/SB/SRW/6-speed man/Big Horn edition (sold)

Posted By: readytoretire on 03/10/04 09:38pm

Florida Cracker,,

If this was the first time you fired it up in a while there may have been some crud in the carb that sucked through,, I have seen them do this before after setting for a long time, the float bowl dries out and gets a flaky residue,, running it getting it hot then letting it set may have softened everything up an flushed it through..

Good Luck

Doug & Elysha & All the Boys
94 Bounder 36'P Diesel Pusher, Cummins 5.9, Osh Kosh Chassis 89'vette, 98'suburban, 04'aveo
3- Shifter Karts = 125mph Fun.:">

Posted By: Stan Birch on 03/10/04 11:12am

Although the governor adjustments *might* be outta whack; that's a rather remote consideration. As others have said, it's probably a gummed up carb messing up optimum mixture parameters. And living in Florida, this happens a whole lot sooner than in cooler climates.

The best initial approach, is to disconnect the fuel line and attach another hose inserted into a gallon of gasoline heavily laced with carb cleaner; and run it for an hour or two in an effort to get rid of the gum.

'99 Winnebago Adventurer 32T, Ford V-10
'00 Yamaha XT 225

Posted By: leisureman2004 on 10/19/04 02:49pm

Mr Ed, What was the dealer in San Antone ? We will be heading south this winter and if I can't mine fixed in NH, it sounds like that one knows what their doing.

Posted By: Vulcanmars on 10/19/04 06:43pm

I bought used a 2002 toy hauler. The 4k Onan only had 5 hours on the meter. It would surge just like yours. Did the norm, plugs, filters ,oil change... Then pulled the carb. OH MY GOD. I have an 8 year old mower that was cleaner than the Onan carb. Cleaned it up and runs like new. Get the rebuild kit it pretty complete.

04 V10 F250 SDCC 4X4
2016 Wildwood 32BHDS

Posted By: leisureman2004 on 10/22/04 09:34am

Very interesting. Mine is a 2800. I've not seen any referencs to a kit available or that it's fixable by an owner. All reference is to an authorized dealer doing any service work. Are instructions included with the kit ? Thanks for your help.

Posted By: Vulcanmars on 10/24/04 08:41pm

Sorry for the delayed post.( Biketoberfrest)
I bought the carb kit localy from an Onan parts dealer. Can't remember the name. Mine is a 4000 series.(not the new in a box type)

The kit only came with a few notes."This gasket if metal" etc. I found the carb easy to work on but I'm a wrench by trade and I have the service manual.
If you can clean a carb on a riding mover you can handle it. Just be gental on the plastic parts.

Posted By: Jayco's 4 us on 10/26/04 06:00pm

for all you genset owners...stabil...stabil...stabil..itl save you, onans like to oscillate..bc

03 Silverado 2500 HD LS D/A
02 Jayco Eagle Summit 263RKS

Posted By: nodog on 09/26/05 05:54am

I suffered with this same problem of the surging generator. After trying all the suggestions, I carried the motorhome to an Onan shop. They charged me for two hours labor ($180) and said that I would have to have a control board changed out before they could do a tune-up on the generator motor. The board and labor would cost me $800, and then there would be additional charge for the tune-up. Now I'm no rocket scientist, but the control board is on the out-put side of the generator set, and the problem was on the engine side of the gen-set. That being said, I bought a tune-up kit for $60 from Onan. I changed out the parts of the tune up kit and tried running the set after changing each piece. When I changed out the condenser (maybe a two dollar part) the unit ran perfect and is running fine after maybe forty hours of opperation. It makes sense that this would be the problem as the condenser stops the points from arching over before they make contact. Good Luck

Posted By: leisureman2004 on 11/05/04 05:49am

Found out that for a 2800 Onan, the only part available as a repair kit is a gasket. Dealers recommend a new carburator rather than cleaning it.So I tried spraying carb cleaner into the carb a dozen times a day over two days and it now purrs. Thanks for all the input.

Posted By: Clubmaxx on 11/05/04 06:57am

I have an Onan 6.5 as well doing the same thing. I used Stan's fix using a gallon of gas mixed with SeaFoam. I let it run until it it drained the can. Restarted it with ass the breakers off and now runs great. I keep a book of threads that could apply to my rig and highlight the responses that I will want to refer to later. This thread is one of them that made it to my book. Thanks Stan and the rest!

Good luck!

'84 Titan 36' 454, Thorleys, Monroes, Bilstein Steering stabilizer, and 16-months of rebuilding inside and out. Check out the whole rebuild project HERE.

Posted By: CA Rambler on 11/05/04 09:01pm

Sounds like a problem I had with my Onan 4.0 about a year ago. Mine started with a fuel leak. I found that the rubber fuel hoses connecting the metal fuel line to the generator and to the fuel tank had deteoriated. The fuel hose at the generator is about eighteen inches long and the one at the fuel tank is about two feet long. Small pieces of the deteoriated hoses had worked their way into the fuel filter. At the time my unit was about four years old. Recommend you check your fuel hoses and if they need changing take care of that first and then change the fuel filter. It's possible that your new filter is already partially pluged from your rubber hoses. I hope your hose going into your fuel tank is easier to get to than mine. That was quite a challenge. There was just enough space between the top of my fuel tank and the floor of my motorhome to get one hand up in there. BTW if you change these hoses remember to blow out the metal fuel line first. That took care of my problem.

Hope this helps.


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