carburetor springs

[hallschuch]

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?

[Dave S]

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.

[jiott]

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.

[Maverick]

What is the source for these McFarlane springs?
Fred

[hallschuch]

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!

[avidflyer]

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

[jiott]

Fred,
The source for those springs is McFarlane. Go to their website and search for Rotax throttle springs.

[Birdseyeview]

Kitfox also sells the lighter springs

[Delta Whisky]

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".

[Maverick]

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

[jrevens]

I found them on MacFarlane's. What is the difference between these and is there any advantage for one over the other?
Fred[/COLOR]

I think the torsion spring from Van’s may be less vulnerable to breakage from vibration for one thing, but that’s just a guess.

I couldn’t stand the original springs and considered them a PITA, if not dangerous... at least with the original conventional friction throttle control that came with my kit. I had a vernier throttle on my previous airplane and loved it, but I have a few friends who were military pilots and they all strongly preferred friction lock throttles, so I decided to keep what I had and get used to it. I tried the McFarlane springs and then the Van’s ones. Then, when getting some training with Paul at Stick & Rudder, he showed me that the springs had been removed from the carbs on his 914 powered bird that we were flying. It worked just fine. Then I discovered that at least 2 of the Kitfoxes at my airport had no springs... one that was approaching 2400 hours on a 1200 hour 80 hp 912. I removed the springs and carefully tested the balance throughout the range. It was good. I believe that the primary reason for the springs is to keep tension on the cables, as mentioned by others. Depending on the cable stiffness, the way they are run, etc., springs may not be needed to maintain carb balance. I have the dual cable from McFarland as I believe most do now. The idea that the throttles go full if a cable breaks also doesn’t appeal to me. When was the last time you heard of a throttle cable breaking? And what if just one breaks or comes loose? Could you figure out in time what’s happening and shove the throttle full to balance the severely vibrating engine, or would you pull it off and probably make it worse? Just wanted to share my thoughts... I am NOT suggesting anyone else do what I did.

[Delta Whisky]

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

They are tough to find on Van's web site. Should have included a statement to that effect. Try this link: https://shop.vansaircraft.com/cgi-bin/shop.cgi?ident=1608845539-464-441&action=search

EDIT: well, that doesn't work. So - go to their store (I hope this will work: (https://shop.vansaircraft.com/cgi-bin/shop.cgi?ident=1608845539-464-441&action=search)https://shop.vansaircraft.com/cgi-bin/shop.cgi) (https://shop.vansaircraft.com/cgi-bin/shop.cgi)and) and enter " spring-00002-L/R-1 " in the parts search window.

The address in the above line is a good address but for some reason the link is messed up - at least when I save the changes and then attempt to use it.

[Delta Whisky]

John - one for the data base: the gent that built the really fancy (lots of electronic wizardry) Longeasy that made the Sport Aviation cover around a year (or, more?) ago - he built that plane to replace the Glassair he lost due to a broken throttle cable and the engine went to idle. BUT - you do make a really good point I hadn't thought of - what if one of the cables break? Will I recognize it and respond appropriately? Hmmmm, another sleepless night. (Thanks John :o )

[Maverick]

I have he friction lock throttle. I'm fine with it versus a vernier type. What drives me crazy is the throttle creep. Plus, to get the engine to really slow down I have to pull on the throttle to hold it out enough to get to idle, otherwise the throttle tries to go in and speeds up the engine. I've become accustomed to it but, I just don't like it. I'm afraid I might pull a cable free from the locking mechanism on the carb. Will these Van's type of springs help with something like this? It sounds like it might.
Fred

[desertdave]

I have he friction lock throttle. I'm fine with it versus a vernier type. What drives me crazy is the throttle creep. Plus, to get the engine to really slow down I have to pull on the throttle to hold it out enough to get to idle, otherwise the throttle tries to go in and speeds up the engine. I've become accustomed to it but, I just don't like it. I'm afraid I might pull a cable free from the locking mechanism on the carb. Will these Van's type of springs help with something like this? It sounds like it might.
Fred

I got so tired of fighting with the factory springs with the friction throttle setup. I pulled the springs off and have been flying without them for the last 9 months. I ordered the Vans springs today and will give you a full report when they arrive. If I have to fight with the Vans springs I'll switch over to a vernier throttle like @desertfox4 has and raves about.

[Delta Whisky]

Maverick - "Van's springs" significantly reduced the creep factor. I still see a tad bit of creep I if lock the throttle (with normal locking pressure) at idle but only to a point. If I lock the throttle at 1800 rpm, where I've set the carb stops, it will creep to about 2000 or 2100 but the creep stops there. I can now lock it at 1800 will a little more twist on the lock. The real benefit for me is that all creep at flight power settings has gone away. The little bit of creep at idle settings bothers me only on the ground; I don't use the lock in the pattern.

Dave - I'm interested in seeing your report. (How well or if your experience is in any way similar to mine.)

[GuppyWN]

I took my springs off 2 years ago. It was one of the first things I did. I won't speak for the factory but I didn't take the springs off in a void.

[Jerrytex]

Springs off. Works great.