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Calisdad's avatar
Calisdad
Explorer
Sep 17, 2014

Onan Altitude Adjustment

I'm having trouble running our generator at altitude.

It's an Onan Microlite 4000. We live at 3000' and it works fine here but last month we camped at 5600' and it wouldn't run. It tried but just wouldn't do it. I tried adjusting the carburetor altitude tab but it didn't change the performance at all. The tab has markings all the way to 10,000'.

Is there an adjustment on the tab that I can change?

thanks in advance-
Cdad
Class C

7 Replies

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  • Calisdad's avatar
    Calisdad
    Explorer
    Sep 17, 2014
    Well before I got much past the air filter I noticed I was at the lower limit on oil DOH ! Changed the oil, blew out the filter and it purrs like a kitten. I won't know for sure until I take it back in higher country but here's hoping that was the culprit.
  • Calisdad's avatar
    Calisdad
    Explorer
    Sep 17, 2014
    Thanks for the input. The manual just told me the most common problem is contamination so I'll check it out. If I recall there was a part that was easily dropped and lost so I'll be careful and check back with what I've found.
  • CloudDriver's avatar
    CloudDriver
    Explorer
    Sep 17, 2014
    Another data point - We used our Onan quite a few times during a month long stay in the Yellowstone/Grand Teton area this Spring. Altitudes between 6-9,000 feet. No problem starting or running. Didn't even think about the altitude adjustment, which is set for sea level.
  • tpi's avatar
    tpi
    Explorer
    Sep 17, 2014
    Just a data point but I have mine set for sea level (live at 1200 ft), and I've forgotten to reset at 5,000 or 6,000 ft and it started and ran fine. I do think it is best to adjust for altitude and eventually thought of it. Especially going downhill-you don't want it lean.
  • WyoTraveler's avatar
    WyoTraveler
    Explorer
    Sep 17, 2014
    Does it look like it is running rich at 3000 ft? Like previous I think you have other problems.
  • Calisdad's avatar
    Calisdad
    Explorer
    Sep 17, 2014
    Almost a full tank tpi.

    It has 450 hours, recent service (over a year) with new carb and I've run it every month since. Pretty sure its the altitude. I'll have to dig into the manual. Just thought someone else has had this issue.
  • tpi's avatar
    tpi
    Explorer
    Sep 17, 2014
    It won't start at all at 5600 ft? There shouldn't be that much difference between 3K ft and 5600 ft. I'd explore causes for no start other than altitude.

    First would be fuel level in vehicle tank. Near quarter tank or less?

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