Low speed idle mix Rehash.

[Scotsman]

I am trying to tune a Weber 32ADFA on my 77 Spider because of poor idle when cold and decreased fuel economy. The engine starts immediately but idles irregularly and often stops unless I increase revs with throttle pedal or control knob under dash. Once the choke opens after warming, the revs increase and hold steady near 900 and the car runs well. I can adjust revs with the idle speed screw but not with the idle mix screw. Revs stay same even when the mix screw is fully seated.
Should I inspect the mix screw? It looks like I can unscrew it without removing carb. If so, will the spring and O ring come out with the screw or stay in the seating?

Any help would be much appreciated.

Many thanks