gr8flyer55

I agree 100% in the disconnection of those springs!
A case in point here....
If you buy a commercially made engine, built or modified (as most of them are) and adapted for R/C purposes, the mfgr. probably has selected a specific carburetor for the engine. In doing this, they inadvertently have gotten a carburetor with very soft weak springs. I fly only converted weedeater engines with the standard carbs. I tested this theory on my plane by not disconnecting the spring purposely. I used a standard size 49 inch oz. servo on my throttles for years. This combination during the test with the spring connected bowed my throttle pushrod so badly the throttle plate never budged!

So you are comparing apples to oranges here. It all depends on the spring's strength, whether you can leave it, or disconnect it in your given situation. Read all the variables into your equation before taking action is what I am saying here.

John

OldScaleGuy

My Feedback: (2)

I am not a gasoline engine expert by any means but we have never had return springs on our glow engines so why do we really need it on a gasoline engine?

acerc

Glow engine's are made that way because we use rod's. Gas engine's are not. The spring is, as stated before, normally on an engine in a weed eater, chainsaw, edger, etc. etc. Those do not use rod's for throttle, they use cable's and the spring is for return to idle. The spring is also, by design, a shim. It does play a role in keeping the butterfly centered.

acerc

A simple test is, grab one of your engine's. Close the throttle, if not closed, try to move side to side. Nothing right. Now open to full throttle, again move side to side. Even with the spring you can move it by hand. But in use the spring is enough to stop that movement. The reason for this space from closed to open is that the butterfly is oval. When closed it is fully against the barrel of the carb. But when open there is a small gap on the side's between the butterfly and barrel.

airraptor

My Feedback: (66)

you dont use a push rod in you gas planes???
If so you are looking for problems.

Guys like to argue on here. i will always cut my spring from the arm unless the instruction included with the engine say not to.
Why put a big strong servo to operate the throttle and spring lol to me that is just plain going against the grain per say. its not needed so i am cutting it.
Do as you wish.

acerc

Yes I use push rod's, that was my point. The gas carb's were not designed for push rod's, cable pull-spring return. Glow carbs are designed for rods not cable.
As for using a cable on a plane, why not? That's what the carb was designed for!
And I never said oneshouldn't cut the spring from the throttle arm. In my opinion that work's good.

acerc

I personally could care less what anyone does. What work's for one might not work for other's. Spring no spring? Take the spring off, run the engine for 2 hours twice a week and before six months are up you will have problem's. If it is not ran that much odd's are you never will have a problem. But one thing is a fact, every single part of these carbs are there for a reason. If that reason is not needed by someone  then do as you wish. There is only one piece that is not needed on the engine for our application and that would be the idle set screw.

pilotpete2

Leaving the spring in play reduces vibration in the whole throttle setup. No matter how little slop there is in the linkage and the servos thew whole mess can vibrate. The spring, by keeping a gentle load on the linkage will reduce the vibration. This is especially important for those who feel they need metal gears in their throttle servos; as they tend to have more slop to begin with and wear much faster than composite gears.
Pete

Truckracer

My Feedback: (19)

I agree, everyone should do as they wish regarding the spring. But, the whole point of this thread and the chart is to point out that "a big strong servo" is not needed to overcome the spring pressure. Any standard sized servo has more than enough torque to overcome the spring and not be worked even a small portion of what it is capable of. Many will choose a stronger servo or one with more precision and that is understandable given the many styles of flight.

The whole point here is be informed and make a decision based on real information and not just the old wives tales that are so prevalent in our RC hobby! But given that, I do not disagree with anyone's choice regarding the spring thing ....it is their airplane.

Truckracer

My Feedback: (19)

Ace, you know most of the time I agree with you but not this time .... every chain saw I have ever owned in the last many years has had a solid pushrod link between the trigger throttle and the carb. Not unlike our RC throttles actually. They use as cheap and simple of a linkage as possible... even on some of the more expensive ones such as Stihl, etc.

Now weed whackers are another matter and mine have a small cable arrangement.

acerc

That may be, but what returns the throttle to idle. I think the principal is still the same, no?

Truckracer

My Feedback: (19)

You are 100% correct my friend .... you feel the throttle spring when you pull on the trigger. I think one of my very old Mac's has an additional spring but I'd have to look for sure.

TimBle

I set up all my planes carbs to work on a pull rod, not a push rod.
Tell me, what are these problems that i WILL encounter?

OldScaleGuy

My Feedback: (2)

Good information from the guys with gasoline engine experience. I consider threads like this educational rather than arguing.

Luchnia

My Feedback: (21)

I run them both ways, one connected to the spring and another without. I would prefer leaving the spring as designed. It works very nice, there are no servo issues, and the spring can return the throttle if anything happens to the linkage - a nice safeguard. The application we run it really is not a big deal at all.

On chainsaws it was there for throttle return and when I was in the timber business I had a couple springs break and the saws run open throttles. It was very dangerous however we were fortunate and always were able to catch the issue before any major impact. They did not break often, but occasionally it happened.

If nothing else I would leave them connected on the planes for safety and since they don't hurt anything, why not? Another thing we used to do was decrease the springs tension on chainsaws as that would tire your hand down if you were running one all day long. You can weaken them and they still have some tension and can bring the throttle back if needed.

nonstoprc

My Feedback: (90)

The potential problem/danger is WHEN the connection breaks away from the engine throttle arm. Without the spring, it will not automatically return to idle/kill position.

captinjohn

I agree and the spring keeps the viabration from wearing throttle parts. I would like to see somereal evidence of how many servos go bad. I am sure not many at all. Capt,n

Luchnia

My Feedback: (21)

I don't think I have ever heard anyone say a servo failed because of a carb spring. I fly with some guys that have flown gas for many, many years and never heard them say anything about one failing - at least because of the spring pressure.

motomike

My Feedback: (4)

This is an interesting discussion. What I may have missed is: Is the spring there only strong enough to return the carb to idle if the linkage falls off? Is the spring strong enough to return the carb to idle working against the servo gear train with no power applied to the servo? The reason I ask is the comment that lightly forcing a control surface from its detent position with the system up and running or lightly moving a servo till it buzzes will raise current levels well above that of a servo fighting the carb return spring. this makes it sound as if the return spring can only help you in the event of linkage disconnect and not servo failure.

acerc

No the spring is not strong enough to overcome the servo in a servo failure.

Luchnia

My Feedback: (21)

It would only save you in a situation that the linkage broke and nothing restricts it from moving to close the thottle. There is not a lot of pressure on the spring. Some are strong than others, but still nothing significant.

airraptor

My Feedback: (66)

there is no way most anyone would be able to tell if a servo failed because of the load (carb spring) applied to the servo. To me having the spring working against the servo is wasted work. :-) Having the spring is like having stiff control surfaces. yes the servo is strong enough to over come this but why allow it.
Also on the 3D planes it better to stop the engine if a failure of the push/pull rod or cable. if it does return to idle the plane doesnt glide very well with a large prop disc out in the air

Maybe i just am a perfectionest (sp). i like all the surfaces and servo operated items to be as free as i can get in movment. one thing some guys may not like but if you counter weight those large 3D surfaces the servos dont jitter as much and you will see a much lower drain at idle (no stick movement) when the engine is running.

acerc

Last year at Monster plane's, in Lakeland Florida,a pilot had to fly for a little over 45 minute's because he lost his throttle. After running out of fuel and then landing he looked to see what was wrong. His throttle arm had came off the servo. He learned two thing's that day. One, use thread lock on metal geared servo's. Two, leave the spring on. No he did not have an on board kill or on board choke, does now.

Everyone do as they wish, it's your airplane.
I'm done with this thread.
Enjoy!

richbran

As a long time experienced gas engine user (whole ZG range, several 3W engines up to 156cc, BFM engine) I have dealt also with this spring issue. Lóóóng time ago I removed them completely. That proved a bad idea, the spring also holds the throttle valve sideways against the inside of the carb. Removed the valve can vibrate left and right on its axle against both sides and on the long run this wears the valve to the point that it leaks air, You cannot cut the engine any more by closing the throttle.
Later (weak servos and batteries) I just hooked them out, trying to save on bat power.
But for long time now I leave them as is. As already stated before, it takes all play out of the loop, RPM control is more precise. The little extra juice that it costs is just negligible nowadays with good servos and Lipo power.

BTW as a sidestep I did loose throttle control due to servo wear on a 130cc engine. It must have been 4-5 Years in place, which means a few THOUSAND aerotows in my case. Shear luck for me that it happened right after landing. But since 10 Years I use on all my gassers with electric ignition, RC controlled switches, so when I cut the engine (the e-switch runs parallel to the throttle), the e-switch cuts it too. Double safety. In my opinion the ones from Stefan Merz (SM Modellbau: http://www.sm-modellbau.de/shop/inde...fa1e33f3874340 are the best. Light, small, simple to operate.
Forget about the mechanical switches in Yr ignition system, prone to generate trouble and if trouble develops in flight, You cannot control it.
The e-switch, when the equipment is turned off, cuts power too, so You don't loose another Lipo due to low voltage damage because You forgot to switch it off. The engine cannot start (curious kids turn props...) if equipment is not on.

Indeed the only mod I make nowadays is removing the idle stop screw.

airraptor

My Feedback: (66)

A guy with a waiver to fly at monster planes didnt have a on board kill switch. he should not be allowed to fly any plane at a contest/show again. i wonder why the CD allowed that.

Richbran. If the spring holds it agains the side of the carb wouldnt it wear that side out just as fast if it had no spring? What carb how many hours? carbs are what like 30-40 dollars excluding OS lol