Throttle Sticking -- Help

[Norm]

I'm new to the forum and back into flying after a 20-year absence. I just bought an '01 M7 260C and the mechanics and I are puzzled about a sticking throttle. (The mechanics haven't seen it -- just me and my son.)

It happens -- sometimes -- when the plane is shut down and I try to crack the throttle to prepare for a startup. Won't budge. Won't advance at all. However, if I go ahead and start the engine then all is fine. ? Has happened at least 5 times with the old throttle and once now with the new one.

I thought it was the vernier throttle so I had a shop replace it with a new friction lock type (which I thought I would like better, but now I'm not sure). Just got the plane back this past w/end and it's happened once since with the new throttle.

So I took it to another shop and they examined the new throttle cable & housing, and even talked to an engine shop and per their instructions they went inside the throttle / butterfly / mixture / housing / box that the throttle conects to via an arm and found nothing amiss. They checked clearances and all seems fine. I have flown it once since and it was Ok but it doesn't stick every time.

BTW, I'm keeping some throttle IN on my approaches and landing long, just in case it desides to happen when the engine is running.

Any ideas? THANKS.

Norm

[maules.com]

The obvious would be routing of the control because you say it has happened with both types and there is nothing wrong in the throttle body.
If it was only with the Vernier throttle, I would suggest the internal ball and groove are damaged. This often happens when the operater inadvertantly keeps screwing the knob either out, or in, after it has reached it's limit. The last bit of travel should be done with the button depressed if the travel to the stops are not set properly. Same with prop and mixture verniers.

[Norm]

The routing is certainly not a straight shot -- from the knob it goes up to the right and through the firewall near the top and then back down and finds its way to the throttle body. Doesn't seem to be any kinks or tight bends anywhere and I don't think the routing has changed lately -- however, the engine has only about 40 hrs on it since Lycoming had it for the crankshaft AD. Maybe at re-intallation of the engine the routing was changed. ?

Thanks, Jeremy.

[UP-M5]

i had a similar issue on a navajo (IO-540) and it turned out to be the interconnect arm for the mixture adjustment. there is a little thumb wheel to adjust the mixture setting- it was 1/16 of a turn too far and the little linkage went over-center and jammed closed sometimes. your mechanic may have to reindex the thumbwheel and reset the mixture setting.

[Norm]

Thanks. I just called my mechanic and read your post to him. Over-centering is just what he was looking for when he looked at it a couple of days ago. He said (if I can remember this correctly) that there is an over-centering that occurs with the mixture when the throttle has been at full power and is being reduced to maybe 80 - 90% of throttle. He asked the engine shop if this was normal and they said yes. It's strange that the mixture actually moves in a counter-intuitive direction just for a little bit when coming off full power.

Of course, my problem is at idle power settings and the mechanic said that the geometry of the mixture / throttle in the idle position is fine and not close to over-centering.

The mystery continues ... however, I've flown it twice since he had things apart and hasn't happened yet.

Norm

[Flyin'Dutch']

Norm

You may be able to reproduce the problem by moving the mixture in/out with the engine off.

If that is the case you know it is this linkage.

[Norm]

I'll give that a try. Thanks.

Norm

[Norm]

Just a follow-up to my sticking throttle problem.

I've flown it almost 20 hrs since the shop took the F.I. box apart and poked around in there and the throttle hasn't stuck since. They couldn't find anything wrong with the linkage or anything but they must have done something cause the throttle ghost is gone. We probably won't ever know what was causing it.

Norm

[maules.com]

Just to be cautious, you might look at the weld end and fitting end on the 4130 bracket that holds the outer cable sheath under the engine.

[Norm]

Thanks, Jeremy, Will do.