I have a '23 4 cyl. and I learned from a 1928 Automotive Engineering book. Here is the basic method. First, close the needle valve on bottom of carb and then open about 3/4 of a turn. Then, turn the air adjustment (big screw on top) so the screw is even with the little spring that holds it in place. Next, you should start the car and warm it up. My book then says to open the needle valve in 1/4 turn increments, stopping to make sure that the car idles and revs smoothly. When it starts to sputter, stop and maybe even turn it back a little. Mine is adjusted to a little over one turn. Next, open the air adjustment 1/4 turn at a time until the car does not run smoothly. At that point, you are close and can add a little more gas until it runs properly. When I first did this, I wound up with the needle open about three full turns and fouled my plugs. I now have it adjusted pretty well. I am sure that others may have some better tips for this procedure.