Showing how the shape of the shaft and the shape of the hole allow for about 45 degrees of rotary movement of the knob. Shown in the unlocked position ...

... and the locked position.

The control shaft is a bit like a 'cam', this shows the 'heel' or low radius side ...

... and the 'lobe' or high radius side.

Showing the wear as a polished area on the leading edge of the cam 'lobe' ...

... and how the leading edge of the cam 'lobe' has been worn down. In this case the vast majority of the wear has taken place over a relatively short distance, from about 1/4" out (fast idle) to about 1/2 pulled. This cable is off the roadster, and almost all the choke use occurs in that range - pulled fully and held while cranking, immediately reduced to half-way and locked as soon as it fires, then gradually reduced to about 1/4 pulled as it warms up (while driving) unlocking and locking each time.

The spring for the locking mechanism, partially removed, showing the rib in the casting that locates in the slot in the spring. Note also the flat in the threaded portion that locates the cable outer in the correct position in the dash.

The locking 'wedge' revealed by the spring in-situ.

The locking 'wedge' removed revealing the leading edge of the 'lobe' of the shaft.

Probable wear in the flat face of the 'wedge', which is shaped like a Woodruff key. This wear, in conjunction with the wear on the leading edge of the 'lobe' on the shaft, is what causes low spring pressure on the shaft hence failure to lock. Whilst turning the wedge round may aid locking as it will be working on a different face, it probably won't last long. And whilst it may be possible to build-up the top face and bring it back to level (if that face were flat originally) doing a similar job on the shaft is a different proposition. While you are partially withdrawing the cable at the very least to do this, you might as well replace it altogether and just do the job once and for all (or the next 30 years at least).

The carb end of the choke cable on chrome bumper 4-cylinder cars. '1' is the interconnecting shaft for the choke. '2' is the lever on the shaft that rotates it as the outer moves up and down. '3' is the choke return spring hooked into the lever and onto the heat shield. '4' is (just visible) the end of the outer butting up against the nipple attached to the lever. '5' is the cable inner above and below the nipple in the fixed arm. '6' is the fixed arm that is part of the 'U'-shaped bracket that is part of the front air-cleaner mounting. Bear in mind that if the air-cleaner is removed the U-bracket with its arm will have been as well so there will be nothing to attach the choke cable inner to! You can temporarily mount the bracket with the air-cleaner bolts but without the cleaner itself, to give you more room.