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Throttle Springs Revisited

RFSchaller

Well Known Member
I replaced the ROTAX throttle springs with weaker Harbor Freight springs. I always check the right carb spring in preflight. I found it separated today after 110 hours in service. The other one had also separated. The good news was the throttle response was fine without them. I would recommend that anybody using alternate springs do a no-springs runup before flying with them to know they are safe if the springs snap.
 
I replaced the ROTAX throttle springs with weaker Harbor Freight springs. I always check the right carb spring in preflight. I found it separated today after 110 hours in service. The other one had also separated. The good news was the throttle response was fine without them. I would recommend that anybody using alternate springs do a no-springs runup before flying with them to know they are safe if the springs snap.

I wont say the 912 can't run well enough to get you to an airport with no springs, but I wouldn't say it will run fine (that imply's it runs just as well as with springs).

The throttle cables used are "pull only" cables. The system rely's on the springs to move the throttle arms in the "opening throttle" direction. They cables will probably push the arms but not with any level of precision for keeping the carbs synchronized. Anyone who has done the sync procedure knows how small of adjustments are required for final tweaking. The flexible cables along with all of the inherent play in the cable housing will not open the throttles with them properly synchronized.
 
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RF,

If you want the weaker springs I suggest the ones from McFarlane Aviation. Been running them for a couple of years and they work great, and stay in place.

John
 
I replaced the ROTAX throttle springs with weaker Harbor Freight springs. I always check the right carb spring in preflight. I found it separated today after 110 hours in service. The other one had also separated. The good news was the throttle response was fine without them. I would recommend that anybody using alternate springs do a no-springs runup before flying with them to know they are safe if the springs snap.

There are many, many Lycoming and Continental engines flying for decades without springs. So why does Rotax have them? It is because they have no confidence in their push pull throttle cable design.

I have had one flight behind a Rotax and hate those springs, that I know for sure. I empathize with those you who have live with them.
 
A search reveals several excellent threads on this subject. All are worth reading. This is the most extensive one. http://www.vansairforce.com/community/showthread.php?t=79102

I got the weaker springs and am happy with the results. The vibration of a running engine will be a factor in even the weaker springs moving the linkage forward. I am concerned that even the current weaker ones will be suboptimal for RV12 formation flying, however, based on one "lesson."

Also see http://www.vansairforce.com/community/showpost.php?p=492537&postcount=51

Some are doing this as well.
http://www.vansairforce.com/community/showthread.php?t=107048
I'd like to try one before buying one and changing out though.

I really like the quad shown on page 2 of this thread. Even though it takes up some room, if it was smooth the extra mechanical advantage (longer throw, ability to change the cable connection position on the lever) would assist with the spring issue.
http://www.vansairforce.com/community/showthread.php?t=106384
 
I do not believe that Rotax engineers are the dummies that the Rotax anti-spring crowd implies. This is confirmed by the explanation provided by Scott: the strong recoil keeps the carbs in synch better. I personally have only 35 hours "behind these springs" and have not found any major nuisance as long as the friction is adjusted properly. I had initial concerns about the longevity of the friction mechanism (addressed in another thread) but pilots with much longer fly time confirmed there is no issue there either.
 
Scott said it best - -

OEM springs do the best job of keeping the carbs in sync. I have flown many types of single engine planes. Just takes a few times to get used to them. NO BIG DEAL. Trying to defeat the purpose of the OEM springs is a gamble not worth taking. This is a great engine overall. It will last longer if the carbs are sync'd together the best way possible.
 
OEM springs do the best job of keeping the carbs in sync. I have flown many types of single engine planes. Just takes a few times to get used to them. NO BIG DEAL. Trying to defeat the purpose of the OEM springs is a gamble not worth taking. This is a great engine overall. It will last longer if the carbs are sync'd together the best way possible.

Note that I didn't mean to imply that only the OEM springs would work (builder/modifier takes responsibility for changes made).
Just pointing out that the system is not likely to work any where close to how it was intended, if springs are not used at all.
 
There are many, many Lycoming and Continental engines flying for decades without springs. So why does Rotax have them? It is because they have no confidence in their push pull throttle cable design.

I have had one flight behind a Rotax and hate those springs, that I know for sure. I empathize with those you who have live with them.

If the 912 used the same type carb as is used on the Lyc and Continentals you would be right. But it doesn't.
 
I also read about a brand new Zenith 701 with weaker springs installed that went into trees on final, because the engine didn't respond to added throttle.

Be very careful guys.

Best,
 
Good discussion, and I agree with the comments on synchronization. I just posted it so that those of us who use alternate springs are aware they do break. The wire diameter on the HF springs was about half the ROTAX diameter. I don't know about the materials differences.
 
There are many, many Lycoming and Continental engines flying for decades without springs. So why does Rotax have them? It is because they have no confidence in their push pull throttle cable design.

I have had one flight behind a Rotax and hate those springs, that I know for sure. I empathize with those you who have live with them.

David, the throttle springs are not a Rotax design, it is Van's design. I have flown many LSA's with Rotax engines and noon of them have the springs like the RV12. it was a safety design feature.

Peter
 
David, the throttle springs are not a Rotax design, it is Van's design. I have flown many LSA's with Rotax engines and noon of them have the springs like the RV12. it was a safety design feature.

Peter

Actually the springs used on the carbs, on the RV-12, are the springs that are on the engine when it is removed from the crate (supplied by Rotax).
 
David, the throttle springs are not a Rotax design, it is Van's design. I have flown many LSA's with Rotax engines and noon of them have the springs like the RV12. it was a safety design feature.

Peter

The Rans Coyote has springs, I believe Rotax invented the feature on the 912 engine.
 
The Flight Design CT has springs. It also has a throttle quadrant. The throttle is easy to move and stays put. There is no in flight adjustable friction but it can be adjusted on the ground in about 5 minutes. I've had to adjust it once in 7 years.
 
Springs for a critical engine component changed for ones from Harbor Freight? Really.................:eek:
 
Springs for a critical engine component changed for ones from Harbor Freight? Really.................:eek:

Hate to be critical, but I am with you. I have the original cable and springs and just don't really understand what this discussion is about. If it took 5 minutes to get used to this throttle, I don't recall it.:confused:
For the sake of everyone, when you contemplate a mod, consider then re-consider everything you do. If you are not sure, seek consultation from the more knowledgeable. They are here and willing to help.:cool:
 
The springs were a safety feature from Rotax and they do two things. First they help normal throttle operation by helping pull any slack or slop out of the cable and helps both carbs to stay a little more equal.

If a cable or linkage breaks that carb will go wide open and not shut down (like on an approach). If you're flying and your engine starts to shake really bad then one response is to try WOT and if it smooths out then you know a linkage on one carb is broken. This feature will allow you to fly to a safe place and land on your terms. Yes there will be a point you have to shut the engine off, but it is on your terms and place. If you disconnect these springs then if anything happens to the carb linkage your done flying and your landing and not on your terms. I have seen a few people reverse the springs to pull the carb shut and that's another poor decision.

If springs are causing anyone problems then fix the problem not the spring. Some throttle setups in some aircraft aren't the best design.
 
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Carb springs

I recall seeing an ad for weaker Rotax springs. I believe if you called Rotax they could tell you if there are weaker factory springs available.
 
is it rotax or bing? my jabiru has that spring and the throttle cable is solid wire , so it is not to take up slop in that case. and this brings us to the question of why cont. and lyc. don't have them.
 
Yes, Paul, HF springs. When you you are experimental you experiment. If you don't feel comfortable with that then use nothing but OEM parts and make no modifications, but many of us fly experimental for they flexibility it allows in testing our own ideas.

Rich
 
is it rotax or bing? my jabiru has that spring and the throttle cable is solid wire , so it is not to take up slop in that case. and this brings us to the question of why cont. and lyc. don't have them.

Some do.
There is a spring that is installed on some carbs that will move the throttle towards full open if the control becomes disconnected (though that is not the reason the are used on the Rotax carbs).
 
Yes, Paul, HF springs. When you you are experimental you experiment. If you don't feel comfortable with that then use nothing but OEM parts and make no modifications, but many of us fly experimental for they flexibility it allows in testing our own ideas.

Rich

Fine, but I don't believe that "experimenting" with critical engine components is a good idea, especially low-grade components from a cheap hardware store. I think the springs breaking after 110 hours sort of proves my point.........
 
Hi Bob,

Springs aren't as useful with solid wire cables unless the wire actually breaks. The springs work best with stranded cable and the thinner the better. Some cables are so thick they have too much friction in their own sheath or have too much bend in the cable which causes too much friction. That causes carb sync issues. Not all throttle set ups are good nor do some aircraft builders install them well. The push pull set up was usually meant to be a stiffer set up and may not have had rotax in their minds when the throttle cables were originally designed. It has certainly been a mix and match over the years.

It's a give and take scenario at times.

_______________________________________________________________

"and this brings us to the question of why cont. and lyc. don't have them."

Answer, because it's a different MFG. That's all, just a different train of thought. Why do we have Chevy's and Ford's and why aren't they the same.

_______________________________________________________________
rvbuilder2002

"There is a spring that is installed on some carbs that will move the throttle towards full open if the control becomes disconnected (though that is not the reason the are used on the Rotax carbs)."


Then what are they for?


_________________________________________________________________________________________

If springs go bad in 100 hrs. you have another problem to deal with. They should last a long time. You may be missing the plastic insert that goes into the eye to keep the spring from being metal to metal. If springs are setup correctly many will last 1000-2000 hrs. My springs and several at my field have well over 1000 hrs. and 6-9 years old.
 
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Roger,

Yep, 100 hrs is not a good result. I'm looking for a better option.

As an aside, I put springs on the carb of a Continental O-200 in my first home built. The throttle cable broke on the ground which had me headed at the FBO lobby! I shut off the mags, got out to point in a safe direction and limped back to the hangar on the mixture for power control. --- Like I said, EXPERIMENTAL!

I think years of building marginal designs has made me view the 12 as a sophisticated design with margin to accommodate some experimentation. Each builder has his/her comfort zone on the limits. I respect that.

Rich
 
Hi Rich,

There must be an issue so where to cause those to break at such a low hour. Do you have the little plastic insert on the bottom of the spring attachment hole? Where did they break? Mid spring or at the hook?
 
"There is a spring that is installed on some carbs that will move the throttle towards full open if the control becomes disconnected (though that is not the reason the are used on the Rotax carbs)."


Then what are they for?


To make the throttles properly open when using a stranded cable throttle control.
In case you weren't aware, a stranded cable control is not meant to be used in a push pull application. It is meant for pull only. Pretty basic engineering. Been done that way for at least 50 years in the motorcycle, snow mobile, etc., industry (where Rotax original got there start in the engine business ;)).

Considering the amount of effect that adjusting the cable jam nut one flat while doing a carb sync has, it is easy to see that the carbs would never stay in sync if we were dealing with the cable slop that would exist when the cable switched between push and pull.
With the springs always pulling towards WOT, the cables are always pulling towards idle. No slop.....
The springs being available to take the carb to WOT in case of control failure is just a secondary benefit since we are using cables that can break.

So, regardless of what you say, the primary function of the spring is to allow the use of a pull cable.
 
Yes, I have the plastic inserts. I was surprised at where the springs broke. - Right at the point where they passed thru the throttle arm.

I originally posted this info just to give people the benefit of the operating experience. I did not expect all the opinions regarding the wisdom of my choice, and frankly I don't welcome them. A comment directed in general, Roger, not at you. I have always found your posts to be helpful, thoughtful and technically sound.

Rich
 
Hi Rich,

I hope no one takes any of my comments as critical. I'm the analytical type and love to teach and help when I can. I like to figure out problems. So many people have helped me over the decades it's my way of giving back.

I would like to figure out why yours broke. Was it both? Maybe it was possible it was a bad metallurgy batch? Have you replaced them and how much time on them. Usually springs fatigue from excessive vibration, heat or over stretching. I have 4 RV12's that come to me. The ones I have now haven't had any problems.
 
"Little Plastic Things"

Very interesting and enlightening discussion, especially re: the relationship between the need for springs and the use of stranded cable.

Maybe a little thread drift here, but I don't recall any plastic pieces on those springs, either the original ones from Rotax, or the replacement ones I installed from MacFarlane. Sounds like a good idea though, to reduce wear. Did you fellows add these plastic pieces on your own? If so, what material did you use? Or, maybe I am having another attack of "CRS". :rolleyes:
 
"CRS" ? Naw

John,
The "Little Plastic Things" are on the throttle arm, not on the springs them selves. You can see them on the starboard side by looking thru the oil door.

This picture is a comparison between the smaller McFarlane replacement spring and the Rotax spring. The plastic insert on the throttle arm is visible .
P1040296-L.jpg
 
Why TWO Carburators

From reading all this discussion, it seems to me that one might ask why rotax has Two carburators that need to be kept in snyc. Don't some engines manage with just One carburator?

Just wondering
 
hi roger,
from a safety standpoint then [looking at lyc. and cont] on some installations the spring is unnecessary. it is not [the following phrase has been beat to death on another forum]'' an accepted industry standard''.
 
Roger, I suspect the springs broke due to cold working the ends when I created the hook to attach them. The spring cross section was significantly less than the ROTAX springs which probably also played a part.

I bought some reduced tension springs from CPS a few months ago, but they seemed to be just as stiff as the originals. I'll try them.

The throttle arm doesn't take much force to move it, and the short cable length past the end of the support sheath seems adequately stiff lto get the throttles full open if the springs break, but at low power synchronization is an issue without springs.
 
Lessons Learned: [url said:
http://www.ch701.com/webmaster/Jon/deer%20hunting/jon_crash.htm[/url]

There are other factors in this besides those springs. Short runway, decision on when to go around, unfamiliar with acft performance etc... Plus the springs look of the harbor freight variety.

I use the McFarlane replacement springs, which I believe are the same that come with the vernier throttle. They still "pull" forward but not as tight as the originals.
 
Depending on the year engine you have you may have 1 or 2 plastic insert protectors at the spring attachment points. You can see one in the picture above and there should be one down at the bottom too.The bottom plastic insert part #963-010 and the top insert part #963-015.

The cold rolling maybe added to its demise and if the metal was scored during the bend that would have added to its short life span.

Why don't you like the Rotax springs? Too much force and you get throttle creep?
 
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Today I installed the reduced force springs (MacFarland?) from CPS. The creep issue is better than the ROTAX springs but still seems like it will be an annoyance. I think I'll use them until annual inspection in March while continuing to look for a better substitute.
 
In regard to the rotax springs

The stock rotax springs would pull the throttle forward almost instantly if you removed your hand from the throttle if the friction lock was not tight. To me, this was an issue while on the ground. I do not lock the friction on taxi. In flight, it would creep even when locked down. Just an overall pain. The mcfarlane springs still have the pull resistance but not as bad as the rotax. With 90 tach hrs, the springs now have settled in and the only resistance is when the friction lock is "open". The inflight creep has almost,almost disappeared. I plan on instLling the vernier assist to eliminate the creep Altogether.

A caveat:
The rotax springs may also settle in a bit and make the pull less, but I changed them out after 10 hours.
 
Sorry to re-open an old thread.
My 12 has just started flying and I have throttle creep. I have the latest torsion springs per SB 18-03-06 and the Macfarlane vernier assist throttle. It seems liken the new torsion springs are too strong. Anyone else experienced this issue with the new style springs or could I have poor friction in the throttle assembly?
 
Didn't your Macfarlane Vernier assist trottle came with a set of perfect fitting springs. Mine where blue and I have no issues. The org. Rotax springs a way to strong.
 
Harry,

If you have the new style springs and you have creep the issue almost certainly is with the throttle friction mechanism. The only other thing I can think of is excessive vibration, which would bring with it a whole different set of issues.

Did you by any chance take the throttle friction nut off during assembly? There are small parts inside that can be tricky to get back together.

Suggest you start troubleshooting by disconnecting the control cable ends at the carbs and checking friction of the throttle mechanism by itself.

John
 
Johns advice is spot on.

The new torsional springs were designed and tested to match the tension profile of the McFarlane springs but have the benefit of not breaking.

There are a lot of them working well in service with the vernier throttle.

You might have gotten them installed incorrectly so they have to much wrap (though I can't remember if that is possible or not), or your throttle control is not working properly for some reason.
 
The new torsional springs were designed and tested to match the tension profile of the McFarlane springs but have the benefit of not breaking.

There are a lot of them working well in service with the vernier throttle.

You might have gotten them installed incorrectly so they have to much wrap (though I can't remember if that is possible or not), or your throttle control is not working properly for some reason.

They're definitely installed correctly - it would be pretty difficult to screw this up. I haven't dismantled the throttle - I'd seen earlier posts about them flying apart so was careful not to get to that point. I'll talk to MaFarlane about the friction mechanism and see if there's any way to increase it.
 
They're definitely installed correctly - it would be pretty difficult to screw this up. I haven't dismantled the throttle - I'd seen earlier posts about them flying apart so was careful not to get to that point. I'll talk to MaFarlane about the friction mechanism and see if there's any way to increase it.

Actually, it is possible to hook one end of the spring in the wrong location (not under the screw head as intended) but I think that makes the tension lower not higher, so that wouldn't be a cause of throttle creep.
 
Tension Adjustment ball bearing vernier throttle

My RV 12 came with the new throttle, the torsion springs were added later. The combined mechanism works well. I adjusted the throttle "no creep" by using a small spanner wrench on the disk holes inside the bezel to the amount needed for the throttle to be comfortable and usable. Hope this has not been redundant to previous posts. Fly Safely
 
Had a very quick response from McFarlane - recommending replace the Vans torsion springs with the McFarlane springs. I'll try this and see how it performs.
 
I have one pair of original springs from Van's, and a brand new pair of the green McFarlane springs. Will let you have 'em cheap if you want. We're using the new torsion springs with the vernier assist throttle cable, zero creep.
 
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