Throttle Resistance

[StudentPilot479]

Has anyone come across a situation where there is resistance in the throttle cable while the engine is running? Or any suggestions on where to look?

With the engine shut down, it smoothly travels through the full range of motion with no resistance.

In flight, there is resistance from idle to about 1500 rpm where the throttle will spring back to idle. Once pushing past 1500 rpm the throttle moves smoothly, and reducing power is smooth.

Everything is new or freshly overhauled. The initial assumption was the throttle cable was catching on something, but nothing is near enough to the cable to snag on it and it appears in good condition.

 

[DENNY]

Check to make sure the engine mount bolts/nuts front and rear are intact and properly installed
DENNY

 

[Steve Pierce]

Carburetor butterfly contacting the inside of the carb throat. Happen to me, shut down was smooth, engine running and I could not move the throttle very easily. Scary.

 

[StudentPilot479]

Thanks. Talking more with the owner, the carb was overhauled and previously had an issue with the throttle sticking. A mechanic should be out in the next week to check the engine mount bolts, inspect and/or swap in another carb to see if that is the problem, and whatever else they can think of. Thanks for the suggestions.

 

[RaisedByWolves]

I am fighting this right now with a newly overhauled or rebuilt marvel carb. I can not get full stop to stop travel. I adjust it to get travel and fly it and once at idle the throttle won’t move. Re adjust and I can’t get all the way to full.

 

[AkPA/18]

Tom is carb heat being used prior to you locking up?

 

[RaisedByWolves]

Tom is carb heat being used prior to you locking up?

I usually pull it on downwind and then off. If I adjust it to where it hits the stops it locks up. Adjust it after and I can’t get full. This is the second carb that did this recently. I had another one from lycon and it fixed the problem. Went back to a rebuilt carb this last round of cylinder problems and the carb issue is back.

 

[AkPA/18]

The reason I asked is that I had a friend who had a carburetor lockup. It was when he was landing and applied carb Heat at reduced power. The butterfly shaft was machine too big and it would swell with heat. When heat was removed it would go back to normal operation

 

[RaisedByWolves]

Interesting. I flew tonight. No carb heat. Landed pulled up to the pumps and I couldn’t taxi. Getting off idle it was locked up. Of course I took my tools out and the sun was setting. Held pressure and wiggled it and got it to come off idle. Same thing happened when lycon rebuilt the old cub. He sent Steve and I both new carbs. We both had the same problem at the same time. If I remember right one was overhauled by them and one was new from marvel. New carbs fixed both of our issues. I’m away for school and don’t have time to pull mine now. I sent marvel an email.

 

[BC12D-4-85]

Can a hot air gun be used to heat the shaft ends and bushing area externally? Maybe try that to see if there's an interference fit there created by heat or at the throttle plate to bore.

Gary

 

[Steve Pierce]

I suspected vibration. I couldn't move for that last little burst to arrest my decent at touchdown but shut it off immediately ad it was smooth as silk.

 

[StudentPilot479]

We got a different overhauled carb installed today, and the resistance is gone. There is no noticeable play in the problem carb's throttle butterfly and it operates smoothly, but I guess with heat and/or vibrations that changes.

 

[rv6ator]

I am fighting this right now with a newly overhauled or rebuilt marvel carb. I can not get full stop to stop travel. I adjust it to get travel and fly it and once at idle the throttle won’t move. Re adjust and I can’t get all the way to full.

If you have the proper cable, then achieving stop to stop travel is just a matter of experimenting with different adjustments on the rod end and throttle arm. Additionally you may need to reindex the throttle arm. So you have at least 3 places to adjust throttle travel, not counting the rod end at the cockpit end. Some combination of adjustments should allow full stop to stop travel. Be patient, as one adjustment can effect the others.

 

[RaisedByWolves]

If you have the proper cable, then achieving stop to stop travel is just a matter of experimenting with different adjustments on the rod end and throttle arm. Additionally you may need to reindex the throttle arm. So you have at least 3 places to adjust throttle travel, not counting the rod end at the cockpit end. Some combination of adjustments should allow full stop to stop travel. Be patient, as one adjustment can effect the others.

I can get it going stop to stop, working on the ground and idling. Move the throttle full with the throttle lever inside the cockpit, fly it, it will jam just around idle, and the throttle won’t go to full, and it idles around 900. Then re adjust, works like above for one more flight.