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Engine start at 75 degrees, runns rough, very rough, when up to 122 degrees runs smooth and normal. Intake leak sealing up at temperature or something else?
  • Re: Rough running engine

    by » 6 years ago


    Is the rough running repeatable and does it alway smooth at 122F?

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


  • Re: Rough running engine

    by » 6 years ago


    it is repeatable. also, the rpms surge about 1200 rpm up and down. as the rpms go up, manifold pressure goes down. just an observation. once it warms up the engine performs normally, no loss of power or misfires...perfect. I was thinking the O-rings where the manifold attach to engine might be in need of replacement or the orings at the carb attach point. the engine has 597 hrs on it. trying to think of any other info that is pertinent. I think that's it. I appreciate your response.

  • Re: Rough running engine

    by » 6 years ago


    I think a little more troubleshooting and diagnostics are needed to try to narrow the possibilities down.

    If you put carb sync gauges (not electronic) what does it show? Is there a wide vacuum down in the idle circuit?

    Possibly:
    Rule out any possible air leak areas.
    This might have something to do with the gearbox. What is the friction torque? Possibly it needs re-shimming? Cold metal shrinkage at start and then the metal swells slightly after it gets hot? This is just supposition on my part trying to think outside the box some.

    The carbs may need some work. New "O" rings, diaphragm, needle valve, needle & main jet, new gaskets. This all comes in a kit.
    If the rubber carb intake sockets are more than 5-6 years old replace them. Make sure the fuel system and filters are clean.


    Rob or Mark any ideas?

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


  • Re: Rough running engine

    by » 6 years ago


    With engine running; spray starting fluid around the intake system to detect an induction leak. the RPM will change if you hit the leak

  • Re: Rough running engine

    by » 6 years ago


    New developement. Have alot of fuel in the carb tray, right side. Must need a carb kit I suppose.

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