Throtlle goes back to flight idle on its own

[N197BC]

Hi

New to the site and the Super Cub world. I just bought a 94 SC with very low time. But while doing the pre buy I noticed during run up the throttle would go back to idle on its own? Is there a friction adjutment or an issue that would cause this???

Thanks
Steve

[Steve Pierce]

Yes, there is a castlared nut at the base of the throttle handle. Remove the panel and cotter pin and tightened.

[btracy]

Plus check check for the correct parts. There is also a friction washer between the throttle lever and the bracket. When I first took mine apart it just had a stack of washers in it. The one the I got from Univair looked like a piece of gasket paper. Alaska Bush Wheels had some made up that were made of delrin or some such thing.

[WindOnHisNose]

Getting the friction lock just right is a bit of a trick, keeping in mind that you have both throttle handles connected, each contributing to the movement. I have had mine too loose, and have had them too tight. Even now I find that mine creeps back a little bit in cruise, with the vibrations, etc, so that genius, Bill Rusk, pointed out that an appropriately folded piece of paper, or formerly a matchbook, could be gently wedged between the housing and the throttle in order to add a bit of a "friction lock".

Randy

[cubdriver2]

Its fun to sit in the back seat of the J3 with someone who is used to flying something like a Cessna in the front seat. As the rpm drops they add carb heat and as it continues to drop they start looking for places to land till they can't stand it any more and yell " do something " . And I push the throttle forward. Fun to mess with spam can drivers.

Glenn

[mike mcs repair]

Also... Check how the alignment is at carb conection and throttle arm indexing.... It will try to creep to its relaxed position

[Dave Calkins]

For the EXP guys......

install a missile nut in place of the castle nut and cotter key. Drill a hole in the cover panel that will fit a socket that fits the castle nut....voila, an easy way to adjust the friction. PS, a knurled knob could be fabricated that allows in-flight adjustment instead of the castle nut or missile nut, but I have not found it necessary to fiddle with after doing the missile nut thing and periodically adjusting it.

[skywagon8a]

This is my version of a friction lock. The white Delrin knob captures an elastic stop nut in an aluminum base. Between the base and the throttle handle is a piece of old shoe leather. Once set, I haven't needed to adjust it.

[Dave Calkins]

This is my version of a friction lock. The white Delrin knob captures an elastic stop nut in an aluminum base. Between the base and the throttle handle is a piece of old shoe leather. Once set, I haven't needed to adjust it.

Excellent!

[DavePA11]

Its fun to sit in the back seat of the J3 with someone who is used to flying something like a Cessna in the front seat. As the rpm drops they add carb heat and as it continues to drop they start looking for places to land till they can't stand it any more and yell " do something " . And I push the throttle forward. Fun to mess with spam can drivers.

Glenn

That is funny. I'll have to try that one.

[Steve Pierce]

What is a missile nut?

[Dave Calkins]

Steve, MS 21042......from that base number you can select the finish plating and dash number for size.

Are you serious?

http://www.aircraftspruce.eu/Hardwar...STOP-NUTS.html

[Steve Pierce]

Always called the Jesus nuts.

[Dave Calkins]

Always called them missile nuts.

[NimpoCub]

I guess we all have pet names for our nuts. I've heard some funny ones.

[aktango58]

both are different from Randy's Gear Nuts

[On Patrol]

I have the throttle cover off right now and I was about to purchase the felt washer. What is the Delrin you speak of and is it for us non-exp guys.

[Steve Pierce]

It is actually a phenolic material. Same material as the phenolic washers in the 3400 tail wheel.

[jgerard]

It's important to have the special Piper "D" washer behind the castle nut that rests against the tab which keeps it from rotating or you won't be able to set the proper friction. I have seen airplanes with regular AN washers which is incorrect. Look in the parts manual to see how it all goes together.

Sorry I don't have a picture for that area right now.


Jason

[Steve Pierce]

Here are some pictures of the proper installation. The friction washers are Velumoid which is like a thin gasket material, same material used between two wheel halves on a Scott 3200 tail wheel. There is one on each side of the throttle lever.

[skywagon8a]

I have the throttle cover off right now and I was about to purchase the felt washer. What is the Delrin you speak of and is it for us non-exp guys.

John, The Delrin is just for the knob. The friction is generated with the piece of shoe leather. I wanted the friction to be adjustable in flight just "because". And, as you know, this is experimental. Though I would not hesitate to use a piece of old shoe leather on a certified plane for this purpose.

[On Patrol]

Thanks will take a look in the morning John

[Darrel Starr]

Steve, live & learn. I had never heard of the gasket between Scott 3200 wheel halves but there it is on the Bushwheels exploded view. I have had 4 to 6 of these apart and never noticed a gasket. Of course the gasket might have been thoroughly stuck to a wheel half but I don't think so - probably just missing. Function? Probably to prevent Fretting of the wheel halfs as they work against each other. Guess I ought to order a couple of them. Thanks.

[Dave Calkins]

Steve, live & learn. I had never heard of the gasket between Scott 3200 wheel halves but there it is on the Bushwheels exploded view. I have had 4 to 6 of these apart and never noticed a gasket. Of course the gasket might have been thoroughly stuck to a wheel half but I don't think so - probably just missing. Function? Probably to prevent Fretting of the wheel halfs as they work against each other. Guess I ought to order a couple of them. Thanks.

Years ago the Scott representative told everyone to remove that "gasket" and leave it out. It was causing fretting and broken bolts. FYI

[Ruffair]

Thread: Throtlle goes back to flight idle on its own

"Flight Idle".

Must be turbine powered.

[kevin]

What is the advantage of using a delrin friction washer over a velumoid type gasket paper washer?

[skywagon8a]

What is the advantage of using a delrin friction washer over a velumoid type gasket paper washer?

Delrin is more apt to be slippery. I would use a piece of old shoe leather for this purpose, as the tension can be adjusted giving the desired amount of friction.

[SteveE]

Here are some pictures of the proper installation. The friction washers are Velumoid which is like a thin gasket material, same material used between two wheel halves on a Scott 3200 tail wheel. There is one on each side of the throttle lever.

It looks like you have Kirbys plane about ready to go......nice job...

[kevin]

Delrin is more apt to be slippery. I would use a piece of old shoe leather for this purpose, as the tension can be adjusted giving the desired amount of friction.

OK. Thanks. I'll try to get a scrap of leather. Perhaps just like the leather used to protect the fabric where rudder and aileron cables exit the plane.

[kevin]

OK. Thanks. I'll try to get a scrap of leather. Perhaps just like the leather used to protect the fabric where rudder and aileron cables exit the plane.

What should the maximum thickness of this old shoe leather be? I've seen the gasget paper washer before and it is tissue paper thin.

[skywagon8a]

I wouldn't think that thickness would be of any concern. The leather is pliable, does not tear and provides a durable friction generating surface. What ever thickness is available and fits the location should work.

[musket]

Check this drawing http://www.supercubproject.com/drawi...s/A3250023.pdf and then sub-drawings B-B and V-V.

[mike mcs repair]

I NEVER use the old leather type disc, or anything...

whats more important is how the cable end lines up with carb throttle arm, so it is "relaxed" and not in a bind trying to move the throttle arm.......

[don d]

There are was. Taking off in a friends piper pacer and going to demonstrate a short takeoff. Let go the throttle to grab some flaps, throttle came back. Just embarrassing.

[Fortysix12]

I know this is an old thread but what I have found to work very well is a split rubber grommet. I take a razor and slice a bulkhead grommetright down the middle creatring two halves , I choose the one that has the smaller holes same size as the throttle lever stud and , about 3/4 OD. Slice it down the middle and divide them on the front and rear. They seam to last a long time. Most recent build is 4 years, 700 hours.

[Cardiff Kook]

Would a throttle creeping forward (as opposed to backwards) be caused by the same set of issues outlined in this thread?

[frequent_flyer]

Would a throttle creeping forward (as opposed to backwards) be caused by the same set of issues outlined in this thread?

Isn't it standard practice to have a spring on the carb throttle arm that pulls the throttle full open if the control cable breaks? If the throttle moves forward on its own then that spring is too strong or the system total friction is too low.

[av8rtom]

I bought the univair washers and they weren't any better than the worn out ones..., I went to a good tackle shop that rebuilds every kind of reel imaginable and matched up some real drag washers and haven't had any problems since!

[aktango58]

I have had two throttle control failures, including one crossing the mountains late as it was getting dark. Those $.39 cotter pins are worth every penny.

Having the throttle go up in power is much nicer than going down when things come apart.

[Cardiff Kook]

Isn't it standard practice to have a spring on the carb throttle arm that pulls the throttle full open if the control cable breaks? If the throttle moves forward on its own then that spring is too strong or the system total friction is too low.

is this the case?