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).

[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.

[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.

[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!

[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