Mixture Control (GAV)

[Dirtrack49]

Hi all,
My new to me 30 Town Sedan while driving yesterday had the mixture control park itself at what I believe is fully closed. I can not move the control from the closed position. It has a Zenith carburetor. Prior to this current problem, it would continuously vibrate itself CCW to rich.
Any idea's?
Thanks,
Tom L.

[alexiskai]

Sounds like the adjusting needle or something adjacent to it is messed up; the GAV should neither get stuck nor be loose enough to move itself.

[duke36]

Perhaps a new bushing is needed up by the dash, under the tank in the cabin?

[johnbuckley]

lift the hood and grasp the choke driver with a pair of pliers to free off the GAV- you'll probably be able to turn it back and forward by hand control after that initial freeing
It sometimes sticks closed with thermal expansion/contraction.
If continual sticking problems unscrew GAV needle from housing and maybe wire wool the threads in case there's a rough burr. even a new GAV needle as the tip is probably damaged now with being forced into seat. If it continually unscrews with vibration undo GAV housing and check circlip at base and /or fit new GAV housing

[Joe K]

If you remove the GAV "bushing" from the carburetor, you'll notice "fingers" on the inboard end which along with the encircling wire clip, serve as "resistance" to the turning of the GAV.

Picture here.

Modern GAV bushing/housings tend to be a little "irregular" in action. Some don't sufficiently interfere with the GAV needle, others "over-interfere" and impede free adjustment of the needle. Sounds like you had both issues.

One remedy to "difficult to move" is to remove the wire clip. Another is to remove the wire clip, carefully "bend" the fingers outward which can be handily and equally done by use of an ice-pick. The wire clip can be bent similarly and reassembled, or left off.

You may in your adjustments "break off" one of the fingers. I have this on one of my carburetors and even with only three fingers and the wire clip, it now works fine for its purpose.

An older GAV bushing and needle may be "relaxed" over time giving the no-resistance case where the carburetor in time moves to the "wide open" or "fully shut position.

And I have done an adjustment by removing the wire clip and simply choosing a small rubber O-ring of sufficient tension. I used Buna-N because its what I had available, but Viton would be the O-ring of choice now with the alcohol laden gasoline today.

This a case where parts are what we are given by the vendors mostly, and a case where even original parts may no longer be ideal. You have to learn to deal with the issue however best.

Of historical note, Ford recognized the problem and for the Model B carburetor, chose an entirely different friction system for the GAV needle, consisting of a washer and a spring which bears up against a shoulder on the GAV needle. Simple can be REAL simple if one lets it.

Joe K

[Dirtrack49]

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Thanks for everyone's input.
I took it all apart and I believe the problem was as John and Joe stated. There was either a burr or grit of dirt on the fuel adjusting needle threads that caused the needle to not seat properly in the needle housing. After cleaning it up, I put a tiny bit of lube on it and reinstalled. Works good now.
This car has only 250 miles on it since restoration. The needle has been offset since new. Now there is no more vibrating the rod out to overly rich.
Car runs much better. Probably has been running way to rich all along.

Thanks again,
Tom L.