Holly 1920 carburetor adjustments?

The 1920 has a plug you can remove on the metering block on the top that has a brass looking tube (emulsion tube?) That can be cleaned also. I did mine trying to chase a rough idle.

I have also never been able to get my mixture screw to kill the engine. I can turn it in to the point of it killing the engine. But never out far enough on the super rich end. And I have cleaned this carb very thorough. I just get it to the lean shake then set it 3/4 turn rich.

Turns out rough idle was the made in China rotor and cap. Now I have a supply of made in USA n.o.s. and some long tip echlin

Luckily now I have a few 1920 parts in my stash. Like the elusive float and spring.