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Thread: throttle and choke return springs

  1. #1
    Birdseyeview's Avatar
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    Default throttle and choke return springs

    During a recent disassembly of the Bing 64 carbs on my 912ULS I was installing a carb service pack (level 3) changing out all the old o'rings and float needle valves and somewhere along the line I lost the return springs on the throttle and choke levers. I hate it when I lose these little items along the way but it got me thinking about alternative possibilities. The throttle springs were the lighter force ones that Kitfox sells that have little to no rpm creep when idling (unlike the stock Rotax return springs). I saw some discussion on this forum from the 2008-2009 time frame about a number of 912 owners that have just eliminated these throttle return springs all together. I have the McFarland friction lock throttle cable installed (not a vernier type) and it has a multi-stranded cable (not a single stiff wire type) connected to each carb. I recognize that if I eliminate the throttle return springs that there is a remote chance that the engine would not increase its rpm if the cable ever broke, but I'm thinking this is so remote as to not be an issue to lose sleep over.

    Question 1: I'm curious as to the latest thinking and current experience without these throttle return springs. If there is a substantial reason to have these return springs I'll certainly buy and install some new ones but eliminating them does make some sense.

    There was also some discussion in past forum entries about some type of gizmo where you can adjust the carb sync from the cockpit by turning a knob of some type that attached somehow to one of the throttle cable adjusters. I had the impression that this gizmo may only be applicable to lever style throttle assemblies but wondered if such a thing might also exist for my McFarland type throttle cable? Carb sync isn't that difficult but if it could be done while in the cockpit that would be very slick, especially while the engine is running.

    Question 2: Does anyone know if an in-the-cockpit carb sync device exits that is compatible with a McFarland type friction lock throttle cable?

    I have a pull to choke knob next to my throttle knob and I have been unhappy with the force needed to engage it because of the strong Rotax choke return springs. The small round choke knob requires a firm grip and a lot of force to pull and engage the choke. It all works as it should and I like the positive choke return when I let go of the choke but I'm tempted to experiment with some lighter return springs to make it easier to engage the choke.

    Question 3: Has anyone found a choke mechanism and/or a non-standard (non-Rotax) choke return spring that works with less brute force to engage it?
    Larry Olson
    Kitfox Series 6 - 1st Flight Oct 2021
    Tri-gear, smooth cowl
    912 ULS

  2. #2
    Senior Member jrevens's Avatar
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    Default Re: throttle and choke return springs

    Larry,

    I (and I know many others) have eliminated the throttle springs altogether. I tried the lighter ones, and even the torsion ones from Vans. I have the McFarland friction-lock throttle cable also. I've carefully routed and supported the cables to minimize vibration and movement. It works fine for me. I actually really consider the springs to be a safety hazard, and I truly don't like such a non-standard situation where the throttle can move itself under certain conditions. If you have a vernier throttle it's a different story.

    As for the "choke", I use a locking t--handle cable from McFarland that works nicely. You can wrap 2 fingers around it and pull & rotate it very easily. The original custom ring pull cable works well also, but without a locking feature (which allows you to have your right hand free for the throttle, or whatever).
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  3. #3
    Super Moderator desertdave's Avatar
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    Default Re: throttle and choke return springs

    I removed my carb return springs. They drove me nuts as fighting with the throttle while trying to land was counter intuitive to my brain and throttle hand. If the throttle cable broke I would just deal with wherever the power went.
    The choke spring removal is intriguing but a bit hazardous in my mind if your carb cable came loose in flight. It could possibly closed the choke and starve the engine of fuel. Basically you have a 50/50 shot of engine power or un-commanded silence. YMMV
    Dave
    KitFox 6 Taildragger
    912 ULS
    Whirlwind 70” Prop
    Garmin G3x
    All around nice guy

  4. #4
    Senior Member
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    Default Re: throttle and choke return springs

    I got some much lighter throttle spings at the local Farm and Fleet type of store. They don't pull on the throttle hardly at all when I back down to idle. They do keep things snugged up though, and I think that isn't a bad thing. As far as the choke spings, I think you probably want to know for sure that the choke (enricher) is getting to the off position, so I would say springs there are a good idea. Mine feel fairly stiff as well, but they do go to choke position, and the engine starts, so that's good by me. JImChuk

  5. #5
    Senior Member Flybyjim's Avatar
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    Default Re: throttle and choke return springs

    This is an interesting thread, is this the type you are using John?

    separately.


    Vernier-AssistTM Throttle Controls for Dual Carburetor 912/914 Series Rotax Engines
    Innovative design allows a neat, clean installation without a clunky splitter box

    McFarlane invents a new type of vernier engine control


    This new type of control has all the fine adjustment benefits of an old style push-button release vernier control, with the simplicity, responsiveness and jam-proof safety of a friction lock control.

    • Light weight and compact behind the dash
    • Good hand space around the knob
    • Safer - Our roller action cannot jam
    • US Patent No. US 8,485,057 B1
    • Vernier-Assist Assembly Video


    These light weight controls use a patented roller action and do not use a positive lock thread engagement. Coarse adjustments are made by pushing the knob inwards or pulling the knob outwards. Fine adjustments are made by rotating the knob clockwise or counterclockwise. For extreme conduit routing or heavy carburetor load installation, slight inward or outward assist pressure could be required during rotation.


    • Super-smooth friction lock
    • Quality all metal construction
    • High temperature Teflon lined for smooth, consistent control
      (Cheapy controls with poly liners will not tolerate engine temperatures)
    • Available in 4, 6, 8, 12 foot and custom lengths
      • Measured from panel fitting to end of conduit

  6. #6
    Senior Member jrevens's Avatar
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    Default Re: throttle and choke return springs

    Jim,

    No, I’ve got a standard friction lock type. I do like the idea of that “Vernier- Assist” design though. I’ve thought of trying one but I’m too lazy to mess with what I’ve got now.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  7. #7
    Senior Member Flybyjim's Avatar
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    Default Re: throttle and choke return springs

    I get that John, if it’s working why mess with it.

  8. #8
    Birdseyeview's Avatar
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    Default Re: throttle and choke return springs

    John,

    Thanks for the tip on the locking T handle McFarland choke cable. I didn't realize that such a thing existed until you mentioned yours. That should overcome my choke spring issue and eliminate the little cable splitter tube assembly behind the panel that I have never liked. The locking feature is also a big plus so the new cable will be a nice all round upgrade.
    Larry Olson
    Kitfox Series 6 - 1st Flight Oct 2021
    Tri-gear, smooth cowl
    912 ULS

  9. #9
    Senior Member efwd's Avatar
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    Default Re: throttle and choke return springs

    so, since John mentions the vernier assist being a different story. For over two years now I have had my throttle require "firm" deliberate force to actuate. On my trip to OSH I loosened up the friction lock and found the throttle to be much more enjoyable to use except one finding I noted. My throttle creeps open, assuming due to the spring on the throttle linkage at the engine. If I leave the friction lock engaged the fine adjust (twist of the knob) works great. Bottom line, I have to leave the tension in the friction lock so the throttle doesn't creep which adds some resistance to actuating the throttle. Not sure I want to remove the spring but I would enjoy the reduced force needed as when the friction is removed.
    Eddie Forward
    Flying
    SS7, 912iS, Garmin G3X

  10. #10
    Senior Member Slyfox's Avatar
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    Default Re: throttle and choke return springs

    Quote Originally Posted by jrevens View Post
    Larry,


    As for the "choke", I use a locking t--handle cable from McFarland that works nicely. You can wrap 2 fingers around it and pull & rotate it very easily. The original custom ring pull cable works well also, but without a locking feature (which allows you to have your right hand free for the throttle, or whatever).
    I need one of these, what part no. did you use and where did you get it?
    Last edited by Slyfox; 08-23-2021 at 10:27 AM.
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

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