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Thread: Lycoming Idle

  1. #1

    Join Date
    Dec 2011

    Lycoming Idle

    Considering that the RSA fuel injection setup specifies an idle mixture such that an rpm rise at idle of 25-50 is achieved when bringing the mixture control to idle cut off, and further considering that many engine gurus advocate agressive leaning on the ground to prevent lead fouling. Why does RSA make thier reccomendation? Would not it be better combining the 2 schools of thought by simply leaning the idle mixture as lean as possible while maintaining satisfactory throttle response from idle (600) to 1200 ish where the idle circut is no longer in play?


  2. #2

    Join Date
    Oct 2011
    New Hampshire
    I would make the educated guess that the answer is inertia.

    That setup instruction has been used for many years for carburetors, and they work for a wide variety of engines, all of the grades of fuel used, and the density altitudes encountered at the majority of airports. The RSA type design is pretty old at this point and I will suggest that the setup instructions have not been changed in many years, through multiple owners and manufacturers of the units. There is likely no return on investment cost, to the manufacturer, of spending some engineering time to try out a better method and update the instructions. You and I pay for the results and our own tweaking from our budget, not theirs.

    As you note, you can turn that little star wheel that controls the idle mixture until the engine barely runs and both make your spark plugs, and your wallet, happier. That said, if you live in Afton Wyoming, the setting you choose will be different than I use down at sea level New Hampshire.

    So its another case of the educated airplane owner owning the maintenance of the machine.

    Best of luck,


  3. #3

    Join Date
    Nov 2011
    Well said Wes.
    The standard will work everywhere whereas a tweak for home elevation may cause problems at different locations and elevations.
    You tweak it, you deal with the consequences.

    As you Said, Good Luck


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