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Jerry_Amerson1's avatar
Jerry_Amerson1
Explorer
Aug 23, 2015

Onan 4000 Generator Problem

Hey all,
I recently posted that the Onan 4000 on my Fleetwood was roaming and would only stay running if I wedged the Governor open, but that is not the case. I went out today to check the adjustment you all told me about and realized that what I was wedging wide open was the CHOKE!!
This puts a whole different twist on things and tells me that there is a fuel delivery problem. My first thought is to replace the fuel filter and I got the seafoam to run through it as well. I'm testing it without any load so if any of you have other suggestions I welcome hearing them. I will have to order the fuel filter so it will be next week before I get it replaced.

Any help is always greatly appreciated.
Thanks,
Jake
Class C
  • Jerry_Amerson1's avatar
    Jerry_Amerson1
    Explorer
    Aug 27, 2015
    It looks like I can get to the first two bolts holding the carb pretty easy, but I suspect there is a third around the back that may cause some problems. The fuel line looks easy as it's right in front. I really don't see anything else except the choke linkage and it's in back so I will need to get the carb loose before I can get to that.

    Has anyone ever pulled one of these carbs off with the generator still mounted in the coach, or should I go ahead and put a jack under it and drop it down.

    Also, where is going to be the best place to get a new or rebuilt carb.

    Thanks again for all your help.
    Jake
  • WinMinnie02's avatar
    WinMinnie02
    Explorer
    Aug 26, 2015
    I would get it service and build a relationship with them. Buying a used RV has risks thus the lower price. I was fortunate to buy mine new 13 years ago and I take good care of it and make sure I used it. Thank goodness I did not listen to the person at the dealer who told me not to use the generator often.
  • DaCrema's avatar
    DaCrema
    Explorer
    Aug 25, 2015
    If the generator ran fine prior to this and all of a sudden quit I would start by doing the simple things. The sea foam was a good start.

    I would also consider the fuel filter replacement already suggested.

    Have you check fuel flow by disconnecting the line from the carb and running RV? It should run long enough on the fuel in the float bowl to do the test.

    The issue on my 2007 RV was the fuel pump. The replacement is involved but not that hard. Likely to cost less than a carb.
  • mlts22's avatar
    mlts22
    Explorer
    Aug 24, 2015
    With any used rig, especially with low generator hours, I'd just replace the carb first thing. Better that than trying to spend your time running random substances or do half measures.
  • j-d's avatar
    j-d
    Explorer II
    Aug 24, 2015
    Remove and replace is not all that difficult.
    First, STUDY the LINKAGE carefully and Document How it Goes with CLOSEUP Photos. Then...
    One or two T-30 screws have to come out, then air filter off. Disconnect fuel line and electrical connector. Two long 10mm screws through Filter, Blower Housing, Gasket, Carb, Gasket.
    Then put the air filter wingnut on upside down. Use that as a purchase to pry the filter base and blower housing far enough away from the carb to clear the choke and throttle plates. Disconnect Choke and Throttle/Governor Linkage. You've got it in your hand.
  • Vulcan_Rider's avatar
    Vulcan_Rider
    Explorer
    Aug 24, 2015
    Jerry_Amerson wrote:

    I see one post that refers to the carb may need to be taken off and cleaned,


    Guess you missed the one post that refers to Seafoam NOT being a really good cleaner ???
  • tpi's avatar
    tpi
    Explorer
    Aug 24, 2015
    I see one post that refers to the carb may need to be taken off and cleaned, but if I have to remove the carb I may just get a new one and replace it.


    Yes- I had one small carb that had a very stubborn clog in a tiny passage and nothing I could do (parts dip, compressed air) could free it. Maybe some kind of ultrasound treatment would have worked? Ended up replacing it. I have never taken off carb on these generators-but if it isn't too big a job, you may want to pull off fuel bowl (depending on configuration) and check for chunks of varnish-clogging jets and passages. Often this is where it is worst and the problem is obvious.

    Like you, I'd be tempted to put a new one on it and be done-especially at right price.
  • Jerry_Amerson1's avatar
    Jerry_Amerson1
    Explorer
    Aug 24, 2015
    It starts OK, but then it will die if I don't choke it manually. I can wedge a rock in by the choke arm and it will run just fine. This is both under load and with no load.

    So, I'm thinking it's not getting as much fuel as it needs and cutting off the air supply evens things out so it will run. Is this correct?

    I'm ordering a fuel filter today, and have already put some Seafoam in the gas tank and ran the generator for awhile yesterday.

    I see one post that refers to the carb may need to be taken off and cleaned, but if I have to remove the carb I may just get a new one and replace it.

    Thanks for all your help.
    Jake
  • j-d's avatar
    j-d
    Explorer II
    Aug 24, 2015
    Newcomers to this issue may find Jerry's Original Thread useful.

    Let me try to re-cap this:

    Once started (Jerry, does this imply hard starting?), it's hard to keep running.

    Throttle (governor linkage) has to be held steady (to control RPM surging).

    Choke needs to be held closed (as in starting) to keep it running.

    Is that about it? If not, please correct.

    Now, a couple questions:

    Is this Under Load (heavy, like A/C in cooling mode)?

    Or Idle (still same RPM, but little to no load)?

    Or Both?

    What have you done so far, besides tweaking Throttle and Choke?
  • Snowman9000's avatar
    Snowman9000
    Explorer
    Aug 23, 2015
    Sure sounds like dirty jets in the carb. No real harm in trying the fuel filter, but don't get your hopes up.

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