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Throttle Return Spring

Old 10-12-2014, 05:41 AM
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ETpilot
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Default Throttle Return Spring

I am a gas newbie and I am at the point in my build where I will be rigging my engine. I reviewed the Sticky " Newbie to Gas General Information "

Item 7 states to disconnect the throttle return sping. All I have read says to do this. Understandable to me.

However, post 34 in sticky, last section on Servo Selection, paragraph 3, it says do not disconnect the return springs. Use a good servo.

All II have read says disconnect. Now I read this post that says do not disconnect.

Thoughts, comments on this. Thanks.
Old 10-12-2014, 07:13 AM
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ahicks
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There's a big debate regarding this. Both side make a good case. I think the much larger issue is making sure the spring is left in place whether or not you decide to disable it.

Me? I disconnect...
Old 10-12-2014, 07:51 AM
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speedracerntrixie
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+1 I disconnect it as well but leave in place. The carb throttle shaft needs the spring pre-load. There are many options here. The thought is that if you leave it connected in the event of a linkage failure the throttle will come to idle or off. With the use of an IBEC you have the availability to shout down the engine at a flick of a switch so no real need for a mechanical safety. IMO most guys go cheap on the throttle servo so being under load all of the time might shorten the servo life. I emphasize the word might here as I have no evidence of this. When it comes to gassers there is a very wide spectrum of opinions on how to do things. If you want options, ask your question and then select the option that makes most sense to you.
Old 10-12-2014, 08:27 AM
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Originally Posted by speedracerntrixie
+1 I disconnect it as well but leave in place. The carb throttle shaft needs the spring pre-load. There are many options here. The thought is that if you leave it connected in the event of a linkage failure the throttle will come to idle or off. With the use of an IBEC you have the availability to shout down the engine at a flick of a switch so no real need for a mechanical safety. IMO most guys go cheap on the throttle servo so being under load all of the time might shorten the servo life. I emphasize the word might here as I have no evidence of this. When it comes to gassers there is a very wide spectrum of opinions on how to do things. If you want options, ask your question and then select the option that makes most sense to you.
I fully understand : Six of one / half dozen of other ! LOL
Old 10-12-2014, 11:56 AM
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I've done the tests and leaving the spring connected places such a small load on the servo it isn't even worth a consideration. For me there are simply more reasons to leave the spring in place than to disconnect it. I can provide a documentation spreadsheet if requested. Before I did the tests I usually disconnected springs, the tests convinced me I was misinformed at the time.

I have seen the wear and damage that can occur to a carb where the spring is removed. Of course not all carbs are built the same and some will work fine long term if the spring is completely removed or disconnected, some not. Some carbs require the spring to center the carb butterfly in the carb bore, some do not. Simply leaving the spring in place and connected removes all doubt.

Last edited by Truckracer; 10-12-2014 at 12:00 PM.
Old 10-12-2014, 03:57 PM
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In all my readings, I read to disconnect. This is the first time I read to leave it connected. So I posed the question. Since the engine is in warranty I will get the manufacture's recommendation. Then see which option to follow. Thanks for the replies.
Old 10-12-2014, 04:17 PM
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Question, would the throttle return spring being hooked up in place help to minimize wear by keeping any slop in the throttle linkage to a minimum? Like a constant pull to keep vibration out of linkage. Just a idea........... Capt,n
Old 10-12-2014, 07:45 PM
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Originally Posted by captinjohn
Question, would the throttle return spring being hooked up in place help to minimize wear by keeping any slop in the throttle linkage to a minimum? Like a constant pull to keep vibration out of linkage. Just a idea........... Capt,n
no but a few big name TOC pilots used to keep the spring hooked up and ran a cable instead of a push rod. They had it set up so the servo pulled to open the throttle, when the servo relaxed the cable the spring closed the throttle.
Old 10-12-2014, 09:42 PM
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I leave the spring connected and haven't had any issues. Using a cable to open the throttle and using the spring to close is a good idea.
Old 10-13-2014, 01:00 AM
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CARS II
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Newbie here.
I read the same postings on the sticky and keep reading in other places like yourself regarding the throttle spring, I concluded that the load on the servo from the spring was unnecessary, I removed the spring from the throttle arm but left it on the shaft in case it needed the load from it ( my throttle servo is an ultra fast digital JR servo )

Speed is correct, ask and you shall receive then take your pick.
Old 10-13-2014, 04:48 AM
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Originally Posted by speedracerntrixie
no but a few big name TOC pilots used to keep the spring hooked up and ran a cable instead of a push rod. They had it set up so the servo pulled to open the throttle, when the servo relaxed the cable the spring closed the throttle.




I use the same method for throttle set up.works very well and easy to do.
Old 10-13-2014, 06:57 AM
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Originally Posted by speedracerntrixie
no but a few big name TOC pilots used to keep the spring hooked up and ran a cable instead of a push rod. They had it set up so the servo pulled to open the throttle, when the servo relaxed the cable the spring closed the throttle.
This is how PE Reivers used to do it, and he was a real expert. I'll probably start doing any new installs myself this way. I think among other advantages, it would provide a perfectly accurate return to the same idle setting each time. (Virtually no slop in the linkage.)

AV8TOR
Old 10-13-2014, 08:45 AM
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To the original poster:
Here is the deal. What you want to do is the following.

1. Leave the spring in place, however remove the tang from the arm and place it under the throttle arm on the carb.
2. The spring acts as a centering mechanism for the butterfly inside the carb. That is why you need to leave the spring in place, just not the tang.

Very easy to do.

Regards
Glenn
Old 10-13-2014, 10:44 AM
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Originally Posted by av8tor1977
This is how PE Reivers used to do it, and he was a real expert. I'll probably start doing any new installs myself this way. I think among other advantages, it would provide a perfectly accurate return to the same idle setting each time. (Virtually no slop in the linkage.)

AV8TOR
I have seen much discussion on the topic, and I throw in with leaving the spring on. Truckracer produced measurements for the servo draw, and I agree with him and Pe Rievers and several others who leave it on. Me too.

Last edited by RCVFR; 10-13-2014 at 12:04 PM. Reason: correcting typo
Old 10-13-2014, 11:08 AM
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Well, this will probably get me in trouble but.... Everyone seems to think that the spring holds the throttle plate centered and it does not. That spring works in torsion to close the throttle; not in compression to hold the shaft. If it were in compression to hold against the shaft, it would push the shaft and plate over against the other side of the carb; not center it. Some carbs have a "C" clip on the opposite side that helps locate the butterfly plate and shaft, some don't. But in any case that spring doesn't do it. Now I will go along with the argument that leaving the spring on may damp some vibrations and help prevent carb throat wear, but that spring is there to close the throttle, not tension/push sideways against the throttle.

Oh boy, I can imagine the comments on this one....

AV8TOR
Old 10-13-2014, 11:22 AM
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Yep, your in trouble now buddy!!! LOL I recently had a 150cc twin outfitted with a Tillotson carb. There was no spring there at all when I got the engine, just a couple bushings leaving about .020 play. I was not completely happy with the idle so one time when I had the carb off the engine I went ahead and installed a compression spring. The next trip out to the field I could not get the engine started until I opened up the low speed needle. Got the carb dialed in again and the engine idled and transitioned better. If I ever get another engine without a spring, I will be adding it again without question.
Old 10-13-2014, 11:25 AM
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Originally Posted by av8tor1977
Well, this will probably get me in trouble but.... Everyone seems to think that the spring holds the throttle plate centered and it does not. That spring works in torsion to close the throttle; not in compression to hold the shaft. If it were in compression to hold against the shaft, it would push the shaft and plate over against the other side of the carb; not center it. Some carbs have a "C" clip on the opposite side that helps locate the butterfly plate and shaft, some don't. But in any case that spring doesn't do it. Now I will go along with the argument that leaving the spring on may damp some vibrations and help prevent carb throat wear, but that spring is there to close the throttle, not tension/push sideways against the throttle.

Oh boy, I can imagine the comments on this one....

AV8TOR
Well this will be one of the very few times I disagree with you and then only partly. Agree though, quite a few Walbro carbs use "C" clips or other methods to center the butterfly in the bore. These are a very positive means of centering the shaft and the carb could care less whether the spring was there or not. On some of the WT and WJ series carbs, that darn spring is the only thing that centers the shaft when the carb is open. Even disconnecting the spring allows the shaft to float along its length and the butterfly can tear up the bore. Then there are carbs that have a "C" clip on one side and only the spring on the other or a combination of the above. The point here is that Walbro uses many combinations of parts to locate the shaft along its length to center the butterfly. Some will never wear out and it seems some are designed to fail early. Leaving the spring in place seems to help for those carbs that don't have other means of locating the shaft.

This is really one of those subjects that has no real right and wrong ...... everyone just do what works for you. If a carb bore wears and it becomes difficult to find a reliable idle speed and mixture, you know the method used on that particular carb was wrong and a lesson will be learned. I know most things I have learned in this hobby were learned the hard way and I adjusted my methods accordingly. All part of why we are in the hobby in the first place I guess.
Old 10-13-2014, 11:29 AM
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Originally Posted by speedracerntrixie
Yep, your in trouble now buddy!!! LOL I recently had a 150cc twin outfitted with a Tillotson carb. There was no spring there at all when I got the engine, just a couple bushings leaving about .020 play. I was not completely happy with the idle so one time when I had the carb off the engine I went ahead and installed a compression spring. The next trip out to the field I could not get the engine started until I opened up the low speed needle. Got the carb dialed in again and the engine idled and transitioned better. If I ever get another engine without a spring, I will be adding it again without question.
I've added "C" clips to throttle shafts to accomplish the same thing. Also used bushings placed over the throttle shaft between the throttle arm and carb body to locate the shaft in the housing. Usually worked in conjunction with a factory provided "C" clip on the other side of the body. This was a common fix on WJ series carbs.
Old 10-13-2014, 05:10 PM
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Count up the yea's and nays' an there you have it. I keep it on and use either a 4-40 rod or a cable depending on the engine layout, but I prefer the cable set up. I also use a metal gear servo.
Old 10-13-2014, 05:46 PM
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I only have 4 gas engines 20cc to 55cc and have left the spring on now for approx. 6 years. Never had a problem with the 3 metal gear servo or the one nylon a gear on the 20cc. I sure someone has had the same luck on removing the spring..............I say this issue is a toss up filp heads..... keep spring......... tails remove spring.............do what makes you feel right
Old 10-13-2014, 10:32 PM
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I'm on my first gas engine with almost no experience. The spring has so little force on it that the servo doesn't even notice it so it's really a non-issue. I'm leaving it alone. It's not affecting anything so I'm not messing with it.
Old 10-14-2014, 12:05 AM
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If it aint broke dont fix it...if something happens so your throttle cable or push rod snaps, it goes back to idle. never had an issue with it on, dont see the point in messing with a perfectly good system. I see way to many fliers think that they have to fiddle with everything. In the end a good percentage of them end up being bitten on the ass.
Old 10-14-2014, 12:16 AM
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CafeenMan
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Originally Posted by mackeyjones
If it aint broke dont fix it...if something happens so your throttle cable or push rod snaps, it goes back to idle. never had an issue with it on, dont see the point in messing with a perfectly good system. I see way to many fliers think that they have to fiddle with everything. In the end a good percentage of them end up being bitten on the ass.
I knew a guy who was a textbook example of what not to do. He would take something brand new, decide he knew better than the manufacturer and proceed to make it unserviceable.

Case in point. He had a brand new gas engine he had never run. Someplace he read (probably online) that he could make it run better or get more power out of it by drilling a hole in the carb. So he did. He could never get the engine to run. So he's at the field trying to start the engine going on and on about how the manufacturer made this crappy engine and doesn't know what they're doing and if they can't make engines that run they shouldn't be in business, yada, yada.

I'm like, dude, you took a brand new engine and drilled holes in it and you're blaming the manufacturer??? *** is wrong with you?

I knew this guy for years and nothing he had ever worked. I never once saw him get a plane off the ground and that is no exaggeration. In one case he brought a plane to the field he had just finished and it had a square leading edge. He totally forgot to shape it and never noticed it even when was covering it. He wasn't senile or dementia. But he had a rectangular leading edge that was amusing.
Old 10-14-2014, 04:59 AM
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Up to 23 posts now, I rest my case (see post #2).
Old 10-14-2014, 06:43 AM
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Originally Posted by ahicks
Up to 23 posts now, I rest my case (see post #2).
Kinda like an oil thread!

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