Model A's used a lever somewhat like yours on the column to adjust the mixture. I haven't a clue why.
On Model A's the left hand lever was manual spark advance (there was no centrifugal or vacuum advance) and right hand lever was throttle. The mixture adjustment was a knob on the right side below the dash that connected to a rod going down to the carburetor. It served a dual purpose of choke (pull out) and mixture adjustment (turn).
