Onan Generator problem

Discussion in 'General RVing' started by onthebrink, May 7, 2011.

  1. onthebrink

    onthebrink New Member

    Hi all,
    The Mrs and I recently purchased a repo'd 1999 Mountain Aire (gas) motorhome. Everything on it works great with the exception of the Onan Marquise BGM 5500 generator with 169 hours. When purchased the gen would not start. Found the spark plugs in bad shape, a fuel line leak, and oil in need of a change. The unit looked like someone just changed the fuel filter and maybe cleaned the slip rings in a quick attempt to get it working. After changing the plugs, oil, and correcting the fuel line leak the unit starts fine. It will run fine under a small load (tv) but shuts down under a heavy load. (ac or microwave)
    Cleaned carb with Gumout carb spray and problem persists.
    What I found is the gen puts out a steady 125v while not loaded or a small load. Note that I'm using an inexpensive walmart multi-meter, true voltage may vary. When I put the generator under load the generator sounds like it is slowing under the load and the voltage drops to about 110v. After about 30 seconds the generator shuts itself down.
    As an experiment I manually increased the throttle with multi-meter on an exterior outlet while the unit was under load and found I can bring the voltage back to 125v and it will not shut down. (ran microwave for one minute)
    So my question is; Am I right to assume the unit is not responding to a load change and what would cause the gen not to respond?
    Thanks in advance,
  2. snap

    snap New Member

    RE: Onan Generator problem

    James Here is what i would do first. I have two of these gen sets and have had the same problem with both of them. Grab hold of throttle shaft at the carb where the govner rod hooks into it. See if seems to be real stiff to move back and forth. what i have noticed is if they have set around a lot the carb shaft gets gumed up and stiff and the govener has a hard time picking up the rpm so to keep it at 60 hertz. I USALLY spray penatrating fliud around the bell crank on the throttle shaft untill it moves freely. When its running you should be able to just barely touch the bell crank and with little presure make the engine respond . The governer on these units are a very sensitive control and need to able to react to diffent loads one of mine seems to start this every summer and i have to free it up Let me know if this helps????

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