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Thread: carburetor springs

  1. #1

    Join Date
    Nov 2014
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    Sebastian, FL
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    Default carburetor springs

    Hi guys,
    I started my 912 the other day ( for the first time) and took caution to not allow the throttle to be pulled open by the carburetor springs... I'm not sure I understand why those springs exist... is it a common practice to remove them, or do they serve some unknown (to me) function?

  2. #2
    Senior Member Dave S's Avatar
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    Oct 2008
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    St Paul, MN
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    1,833

    Default Re: carburetor springs

    Karl,

    The design purpose of the springs is to assure, that in the event of a throttle cable break or disconnect, the engine goes to full throttle rather than going to idle. The theory is that full throttle is better than no power.

    Using a vernier throttle, which is the normal throttle type used with a 912, prevents the throttle from creeping when set to a specific power setting.

    My understanding is that very few people experiment with removing the springs.

    I have the vernier throttle and after a little getting accustomed to, like it, especially for fine tuning the RPM.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  3. #3
    Senior Member jiott's Avatar
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    Jun 2010
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    Portland, OR
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    2,959

    Default Re: carburetor springs

    Another benefit of the springs is that they keep the throttle cable under a slight tension continuously; this helps keep your synchronization accurate and eliminates any slop or push/pull differences. The lightest aftermarket springs from McFarlane have plenty of tension to do all these things. Many,many of us have changed to the McFarlane light springs. They work well even without a vernier throttle, with just the normal friction nut.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  4. #4
    Senior Member Maverick's Avatar
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    Mar 2017
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    Phoenix
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    Default Re: carburetor springs

    What is the source for these McFarlane springs?
    Fred
    EAA, AOPA
    KF5 (N49FK & N36KJ)
    Phoenix, AZ

  5. #5

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    Nov 2014
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    Sebastian, FL
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    Default Re: carburetor springs

    Quote Originally Posted by Dave S View Post
    Karl,

    The design purpose of the springs is to assure, that in the event of a throttle cable break or disconnect, the engine goes to full throttle rather than going to idle. The theory is that full throttle is better than no power.

    Using a vernier throttle, which is the normal throttle type used with a 912, prevents the throttle from creeping when set to a specific power setting.

    My understanding is that very few people experiment with removing the springs.

    I have the vernier throttle and after a little getting accustomed to, like it, especially for fine tuning the RPM.
    Thanks Dave, I appreciate the info!

  6. #6
    Senior Member
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    Apr 2009
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    Chisholm Mn
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    1,562

    Default Re: carburetor springs

    I replaced those strong springs with some light duty ones from my local farm and fleet type store. They work fine as far as I can tell. I have the vernier style throttle cable, and just a little bump on the button, and the throttle would jump forward. Kind of always seemd to fight it coming back to lower power settings also. I much prefer what I have now. JImChuk

  7. #7
    Senior Member jiott's Avatar
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    Jun 2010
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    Portland, OR
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    Default Re: carburetor springs

    Fred,
    The source for those springs is McFarlane. Go to their website and search for Rotax throttle springs.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  8. #8
    Birdseyeview's Avatar
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    Sep 2017
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    Oregon, Ill
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    198

    Default Re: carburetor springs

    Kitfox also sells the lighter springs
    Larry Olson
    Kitfox Series 6 - 1st Flight Oct 2021
    Tri-gear, smooth cowl
    912 ULS

  9. #9
    Senior Member Delta Whisky's Avatar
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    Dec 2017
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    Amissville, VA
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    637

    Default Re: carburetor springs

    After being frustrated by this same problem and spending way too much time on the internet, I discovered that Vans Aircraft had the same feeling. They designed and now sell a spring to replace the Rotax original. It is a torsion spring and works great. Takes about 10 minutes to install. Look for P/N "spring-00002-L/R-1".

  10. #10
    Senior Member Maverick's Avatar
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    Default Re: carburetor springs

    Quote Originally Posted by Delta Whisky View Post
    After being frustrated by this same problem and spending way too much time on the internet, I discovered that Vans Aircraft had the same feeling. They designed and now sell a spring to replace the Rotax original. It is a torsion spring and works great. Takes about 10 minutes to install. Look for P/N "spring-00002-L/R-1".
    I have searched for this part number on Vans website. I have been unable to find it. I reviewed SB 18-03-06 in the hope of finding a link to the parts to no avail.

    I found them on MacFarlane's. What is the difference between these and is there any advantage for one over the other?
    Fred
    EAA, AOPA
    KF5 (N49FK & N36KJ)
    Phoenix, AZ

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