Time to rebuild?

1/8" open sounds about right, since that is how far the choke pull-off is supposed to pull it open. You can play with the choke's thermostat adjustment. There are rich (R) and lean (L) marks to tell you which way to rotate it. Don't fool with the idle mixture, since you want that correct when the engine warms up. If it doesn't stall or stutter before it warms up, you are doing about the best the system ever did. Chokes were always inexact, and why they kept kludging on additions to try to improve them. You will never get it as smooth as modern fuel injection, or even 1980's electronic carburetors. In the 1950's, the driver had a manual choke cable, and teaching most drivers how to adjust that as the engine warmed was difficult. My mom never quite understood what the choke or clutch did and was lucky to muddle through, often stalling at red lights, then saying, "Oh, I forgot I'm supposed to push in the left pedal when I stop".