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Thread: O.S.61SF


  1. #1

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    O.S.61SF

    Bax
    I cannot get this engine to make a transition from idle to full throttle b/c when idling it is loading up with fuel. I have replaced all 3 o rings on the mixture control valve , cleaned the carb parts good, but still setting the mixture contol value as lean as possible , I still cannot get smooth transition. After a minute of so of idiling it loads up with fuel so much that smoke and fuel blow out of muffler. At full throttle I get good response, a little rich, and at idle I have good response but cannot go from idle to full throttle unless I increase a little at a time. I cannot get the low side lean at all. Leaning the top to the point of engine stalling helps the transition some but then my top end is too lean. A new OS glow plug #8 was installed and fuel is good.

  2. #2
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    RE: O.S.61SF

    What size propeller are you trying to use? What exhaust system are you using? Are you using a pump? How is the fuel tank positioned with respect to the center of the carburetor?

    We need more information in order to answer your questions.

    Thanks.
    Bill Baxter, Manager Hobby Services/Futaba Service/North America
    3002 N. Apollo Dr. Ste. 1 Champaign, IL 61822 USA
    Service Phone: 217 398-0007
    Email: hobbyservices@hobbico.com

  3. #3

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    RE: O.S.61SF

    Bax, I am using a 11x7.5 nylon{Master Airscrew} Stock O.S. muffler, not using a pump, and the fuel tank is centered behind the carb and slightly elevated.

  4. #4
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    RE: O.S.61SF

    OK. The fuel tank should be mounted so that the centerline of the tank is no higher than the centerline of the carb, but can be as much as 3/8" lower.

    Loading at low throttle settings usually means that the idle mixture is too rich or you have too much fuel pressure. If you have a check valve in the muffler pressure line, get rid of it. The fuel tank must depressurize when the throttle is retarded.

    You may also be trying to idle at a too-low RPM. Anything lower than 2,500 RPM would be considered good. You need to balance the idle RPM with the idle mixture.

    You may need to take the engine out of the model and put it onto a test stand to get things sorted out. If the engine will run "all day" on the test stand, then there's nothing wrong with it at all.
    Bill Baxter, Manager Hobby Services/Futaba Service/North America
    3002 N. Apollo Dr. Ste. 1 Champaign, IL 61822 USA
    Service Phone: 217 398-0007
    Email: hobbyservices@hobbico.com

  5. #5

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    RE: O.S.61SF

    W.P.
    Where did you get the 3 O-Rings from. I have been looking and cannot find them anywhere.

    Steve

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    RE: O.S.61SF


    ORIGINAL: Steve Haas

    W.P.
    Where did you get the 3 O-Rings from. I have been looking and cannot find them anywhere.

    Steve
    Towerhobbies has them. O.S. O-Ring I Valve #6-8H/#7L/#7M LXCS00 O.S. O-Ring IV/PRC #6H Rubber LXCS01

  7. #7

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    I recently purchased a used airplane with the O.S. .61SF on it and am having the same issues.
    Did you get it resolved? Do you have an instruction manual for this engine? I have seen this type of idle mixture control in the past
    and it is a pain to adjust. Which way do you move the mixture control to lean and which way do you move it to richen the idle mixture. Mine has the same
    issue of not taking throttle through the mid-range.
    I love the smell of buring two stroke oil in the morning.
    AMA 1548
    IMAA 18995

  8. #8
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    The mixture adjustment for the idle turns clockwise to lean, and counter-clockwise to richen. If the engine won't transition from idle, the issues mentioned above all hold. Resolve them, and barring a worn needle or piston/liner fit, you should solve the difficulty.

    To get an electronic copy of the O.S. Max .61 SF-series manual, please send an email to enginesupport@hobbico.com
    Bill Baxter, Manager Hobby Services/Futaba Service/North America
    3002 N. Apollo Dr. Ste. 1 Champaign, IL 61822 USA
    Service Phone: 217 398-0007
    Email: hobbyservices@hobbico.com

  9. #9

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    Thanks for the information. I will set up and make adjustments accordingly.
    I hope this cures the ills of the engine.
    I love the smell of buring two stroke oil in the morning.
    AMA 1548
    IMAA 18995


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