throttle and choke return springs

[Birdseyeview]

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?

[jrevens]

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).

[desertdave]

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

[avidflyer]

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

[Flybyjim]

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

separately.

https://www.mcfarlaneaviation.com/media/images/valogo-web.jpg
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 (https://www.mcfarlaneaviation.com/articles/vernier-assist-assembly-video/content/)Assembly Video (https://www.mcfarlaneaviation.com/articles/vernier-assist-assembly-video/content/)


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.
https://www.mcfarlaneaviation.com/media/images/includeimages-va-throttle-function.jpg


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

[jrevens]

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.

[Flybyjim]

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

[Birdseyeview]

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.

[efwd]

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.

[Slyfox]

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?

[jrevens]

I need one of these, what part no. did you use and where did you get it?


Hi Steve,

They’re made by McFarlane. You can buy the dual cable for the Rotax and then the T- handle for it.

[Slyfox]

great thanks, went to there site and found what I needed. thanks

[Shadowrider]

I also removed the springs as I think they are a safety issue. Last thing I want is throttle going WOT especially at cruise having an engine runway past red line ending up in a pieces. I also installed the vernier throttle. They are my favorite. I use the twist feature all the time to adjust power and it is very accurate. Pricey, but quality built.

[Jerrytex]

Another vote for taking them off.

I Took them off my KF 4 and used the standard friction throttle. Worked/works fine. I plan on taking them off on my new build as well.

[3kdscf]

I also removed the springs as I think they are a safety issue. Last thing I want is throttle going WOT especially at cruise having an engine runway past red line ending up in a pieces. I also installed the vernier throttle. They are my favorite. I use the twist feature all the time to adjust power and it is very accurate. Pricey, but quality built.


First ,time for a TeamKitfox Forum appreciation moment. In the pre-internet days, getting information like that found on this thread was difficult and time consuming. Who knows how many lives easy access to this kind of information has saved. Enough gushing.

My Series 6 is a year old with 170 hours on it. I have the stock 912ULS throttle springs and agree, its really dangerous. Even with my hand on the throttle every second during base and final, it sometimes slips in my sweaty hand and goes to full throttle. Even when the throttle is locked tight at 2000rpm on the ground, it slowly creeps up in RPM.

I will look into the weaker 6822 springs used by the Vans RV-12 as well as the Vernier-Assist throttle. I know the strong springs insure the throttles stay synced but for me, the risk of a full power surprise at an inopportune time is more dangerous.

My plan is as follows:
1) try the vernier assist throttle with the stock strong springs, if that doesnt work ...
2) replace stock throttle springs with the weaker 6822 springs, if that doesnt work ...
3) take the springs off entirely and make sure cables are solidly supported entire length to minimize sync problems

Thanks everyone!

[DesertFox4]

I believe McFarlane’s Rotax vernier throttle set up comes with the less aggressive springs. If not, order them at time of throttle purchase and install them right away. You won’t enjoy the stronger springs. Model 6’s take a different length cable compared to a model 7.
I love my McFarlane vernier throttle system. Just be mindful not to loosen the friction wheel too much and pull the cable insides out.
Little parts fall out. Luckily McFarlane has a video how to reinstall the little bits if you don’t lose any bits down your center console’s flap handle cut out.😢

https://www.mcfarlaneaviation.com/products/category/rotax-controls/

Vernier version:
https://www.mcfarlaneaviation.com/products/category/rotax-controls/

Chose knob style, cables do not usually include a knob.
https://www.mcfarlaneaviation.com/products/product/6620/


https://youtu.be/5RcjEd7lR4Q

[3kdscf]

I believe McFarlane’s Rotax vernier throttle set up comes with the less aggressive springs. If not, order them at time of throttle purchase and install them right away. You won’t enjoy the stronger springs. Model 6’s take a different length cable compared to a model 7.
I love my McFarlane vernier throttle system. Just be mindful not to loosen the friction wheel too much and pull the cable insides out.
Little parts fall out. Luckily McFarlane has a video how to reinstall the little bits if you don’t lose any bits down your center console’s flap handle cut out.😢

Thank you! You saved me from buying a duplicate set of springs :) I see now that it says that the throttle comes with the 6408 hardware kit which includes the springs.

Does anyone happen to know the ideal throttle cable length for the series 7? I have a series 6 but its a 7 firewall forward. I measured my existing throttle as well as I could while it was still installed and it appears to be 42". I did note that the product literature says "easy to trim to length" so I could just order the 6' one and then trim it to the same length as my existing throttle but if the 48" would work unmodified, I would rather let the factory de-burr the end of the coiled spring housings :)

[efwd]

My SS7 Vernier throttle is stock as it arrived from Kitfox. It's just a matter of routing it. Mine worked out without any modification.

[DesertFox4]

Eddie, thanks for your last post.👍
I purchased my cable also from Kitfox Aircraft.
They have them listed on page 23 of their parts manual.

[wibblewobble]

I also have the Macfarlane vernier throttle on my 4 and find it perfect with the weaker springs.
Anyone heard of the in cockpit throttle balancing gizmo? Sound a great idea

[Av8r3400]

I also have the McFarlane cables for throttle and enrichener. They are expensive but worth every penny.

I also post this often in the cable threads, but this is the best method of "cutting" these cables to keep them from fraying.


https://youtu.be/LnTHZhTkg2U

[3kdscf]

I also have the McFarlane cables for throttle and enrichener. They are expensive but worth every penny.

I also post this often in the cable threads, but this is the best method of "cutting" these cables to keep them from fraying.



Cool trick!!!! Thanks!

[3kdscf]

Eddie, thanks for your last post.👍
I purchased my cable also from Kitfox Aircraft.
They have them listed on page 23 of their parts manual.

Thanks! I didn't realize that Kitfox sold these. I did look at the catalog but the only vernier throttle mentioned was for the 912is (Kitfox Part # 99004.000). I would much rather give my business to John ... and get one already pre-cut to the right length :)

[jiott]

I am really curious about all the talk about vernier throttle cables. I have never personally ever found the need or want to adjust my engine speed to the very fine degree possible with a vernier type throttle. The standard friction screw knob gives me more than enough adjustability. Just for my own education, I would like to hear what phases of flight you guys feel the vernier is an advantage? This is an honest question; I am not trying to trash the use of a vernier because obviously a lot of folks seem to prefer it. Maybe I could improve my flying with a little education, especially from those who have tried both on the same airplane and prefer the vernier.

[Shadowrider]

I have flown both. 90% of the time I am twisting the throttle. Vernier is the best way to go. Only time I am pushing and pulling the throttle is takeoff and landing. Vernier is much more accurate at adjusting rpms and manifold pressure. John, on a NA engine its not as big of deal because throttle is not as sensitive. With a turbo, I wouldn't run anything different, especially with a fixed pitch prop. You would be all over the place. The mcfarlane is nice because you can push and pull the throttle quickly, without pushing a button, and then you can twist it to give it an accurate adjustments. Turbulence they are nice. Updraft I give it twist out, down draft 2 twist in. Once its smooth a twist back and its right at 5200rpms:) I also like them for starting up. Pull throttle out then two twist in and she starts up 2000rpm every-time.

[3kdscf]

I am really curious about all the talk about vernier throttle cables. I have never personally ever found the need or want to adjust my engine speed to the very fine degree possible with a vernier type throttle. The standard friction screw knob gives me more than enough adjustability. Just for my own education, I would like to hear what phases of flight you guys feel the vernier is an advantage? This is an honest question; I am not trying to trash the use of a vernier because obviously a lot of folks seem to prefer it. Maybe I could improve my flying with a little education, especially from those who have tried both on the same airplane and prefer the vernier.
I have the 912ULS in a Kitfox 6 with a series 7 firewall forward. The reason I am making the switch is that the factory provided throttle cable, even when clamped down as tight as I can turn it, slowly creeps up in RPM. It does this at cruise RPM but way more annoyingly at idle. Trying to do a pre takeoff checklist when you have to keep taming the engine to keep it from roaring can be pretty distracting. What I am really describing here probably has nothing at all to do with the throttle and everything to do with the really strong springs. I probably could have solved the problem with just springs but I decided that while I was at it, I would replace the throttle as well because I like the vernier idea. The big use for the vernier for me personally would be for cruise RPM. It often takes me several tries to get the RPM I want at cruise whereas with a vernier, it would just be a quick twist.

[avidflyer]

I have the veneer style throttle on my Kitfox 4 with 912. I really like it, I did install weaker springs as well. Usually I will grab the throttle ball with my first and second fingers, and when they pull, the button is pushed in when it pushes against your palm near the bottom of the fingers. It is very nice for larger throttle changes. For a small change in throttle setting, the twisting of the ball works very nice. I do have another friction lock throttle, but even though I'm a bit on the frugal side, I'll buy the veneer throttle for the next project. I would say though that weaker springs will go a long way to making what you have tolerable. Here is a short video of my first flight I did in the plane, and you can see how I held the throttle. Of course in cruise, I'm not usually holding the throttle, this was just up and around and down, and I don't use the twisting motion much. Please excuse the cheap chinese gopro camera copy. Sound out of sync, and picture quality not near as good as the real deal. JImChuk
Kitfox 4 first flights after rebuild panel view - YouTube (https://www.youtube.com/watch?v=bw6SMCcaAxo&t=3s)