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Fuel mixture high altitudes

in 912 / 914 Technical Questions 9 years ago
High group,
i have heard that the Bing carburetors do well adjusting the mixture at altitudes below 6000 ft. but do not do such a good job above that. is that generally true and if so are there any workarounds for this problem?
Mike

  • Re: Fuel mixture high altitudes

    by » 9 years ago

    Hi Mike,

    Some of this answer can depend on your home field elevation and your average flight altitude. A fairly good place to be for a ground adjustable prop is to have the wide open throttle (WOT) rpm around 5600-5650 RPM in flat and level flight at WOT and at your average altitude.

    First thing is to make sure your prop pitch is set for your average altitude.
    If you live at sea level and never fly over 2-5K ft. then leave the needle alone. If you live somewhere with a high field elevation or always fly up at 7-11K ft. then lean it a notch on the needle.

    Bing's do a fairly good job so always tinkering with the needle and main jet isn't necessary for the average user.

    This should get you in the ballpark.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: Fuel mixture high altitudes

    by » 9 years ago

    How does this discussion relate to the 914? Since the 914 has boost, does that mean that there is no need to adjust the needle, even if the base is sea level and a lot of flying is 8,000 - 10,000?
      
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  • Re: Fuel mixture high altitudes

    by » 9 years ago

    Thanks Roger,
    Good information...the reason i was asking is that I may be moving to "high" country where the home airport is 8000'...performance on TO would then become a mater of some concern. I have read about the HACman manual leaning modification...what are your thoughts on that mod?
    Mike
      
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  • Re: Fuel mixture high altitudes

    by » 9 years ago

    Forget you ever heard of Hacman. I know several people who have tried it and put it back to stock.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: Fuel mixture high altitudes

    by » 9 years ago

    Have done all kinds of tests with high altitude jetting 912s 5000 to 14,000 msl from here 5000 to a friend in colorada whos base is at 7000. Finally ended up bringing my needle jet back to stock and went went from stock 155 to 150 main jet at 5000 airport base 1 point per 1000 feet. No increase in power but brought egt from 1250 to 1350 so this is where i have ended up. All that testing and hassle with little results. The carbs do a pretty good job stock as is.
    Thank you said by: Rhett Mitchell
      
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