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Mixture Knob Rotating On Its Own

The adjustment knob on my mixture cable is rotating inwards during flight. I set the mixture at cruise, then watch the knob rotate inwards enrichening the mixture and requiring constant adjustment.

I don't see a friction adjustment or way to firm up the rotation pressure to prevent it from rotating with the engine vibration.

The cable is OEM and less than a year old, the knob is by Performance Aero.

Any ideas?

Model: Bonanza 36
Aircraft Serial Number: E-26
Posted 11/29/2023 - 3 months ago
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(In this discussion, directions are given from the pilot seat looking forward past the spinner; keep this in mind when I say forward and aft, clockwise and counterclockwise.)

At the base of the mixture control is a knurled nut, generally a couple of detents on the aft face. First, using a wrench to grab the detents, loosen the knurled nut a couple of turns. The reach forward of the instrument panel to access the forward nut, turn it clockwise - away from you - one flat, then re-tighten the knurled nut. Now you have an excuse to go flying and try it again to see if you need more or less.

There is a packing under the knurled nut, and the panel distance between the nuts is a fixed amount, so if more of the control housing is moved aft, there is less room for the packing, and it tightens down on the control shaft. Moving the forward nut forward even 1 flat (1/6 of a turn) is quite a bit of squish on that packing.

Mike
ABS Technical Advisor

Posted 11/29/2023 - 3 months ago
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Mixture Knob Rotating On Its Own