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Throttle Slowly Opening When Engine is Running

in 912 / 914 Technical Questions 8 years ago
I suppose this isn't specific to the Rotax but I've been doing some taxi tests in anticipation of my inspection in a couple of weeks and I find that the throttle cable gets slowly pulled forward by the spring on the carbs if I let go.

Looks like the spring is too tight, pulling it in ? Curious if this is unusual and what the fix might be? Is there a way to make the spring pull less? Or is that the wrong approach!

Thanks

Paul

  • Re: Throttle Slowly Opening When Engine is Running

    by » 8 years ago

    The spring is there to intentionally open the throttle in the event of a cable break (or disconnection). You might look at the friction settings on your throttle.
      
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  • Re: Throttle Slowly Opening When Engine is Running

    by » 8 years ago

    +1 on Jason. The spring also serves to maintain a level of tautness on the throttle cable system thus enhancing throttle response. On some aircraft, you can replace this style of "push-pull" throttle cable with a combination "push-pull" / vernier-assist throttle -- see: https://www.mcfarlaneaviation.com/products/category/rotax-throttle-controls-panel-mount/

    If you are a S-LSA, you need the aircraft manufacturer's approval to make this change.
      
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  • Re: Throttle Slowly Opening When Engine is Running

    by » 8 years ago

    As mentioned tighten your throttle friction. Many RV12 owners and a few other MFG's used a cheap throttle and many went to a better McFarlane throttle and that fixed the problem.

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

      
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  • Re: Throttle Slowly Opening When Engine is Running

    by » 8 years ago

    A +1 to everyone!

    If the throttle cable were to let go in flight, Dealing with the throttle stuck open is less exciting than one that drops to idle.
    You can alway fly to the destination and then kill the ignition to make a dead stick landing.
    That is the lesser evil compared to an Off Field landing with an otherwise perfectly good engine.

    This is also a good time to remember why there must ALWAYS be someone competent in the cockpit whenever the engine is operating.
    Imagine the nightmare of your plane powering up by itself on the ramp with no one in it!

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
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  • Re: Throttle Slowly Opening When Engine is Running

    by » 8 years ago

    I recall a "recall" on some of the springs for the Rotax. They were breaking prematurely. the new spring also has less tension and I think I got them from Kitfox. Cant remember.
    Many Kitfox pilots take the springs off completely because they use a stiffer cable than the floppy original. The McFarlane throttle is a great control cable and gives nano adjustment capability. Bill speaks correctly about the spring being a safety issue. An open throttle is not actually a bad thing in the hands of a competent pilot. It is much preferred to the dead stick alternative for lack of a three dollar part.
      
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