The air correction jet is the most mis-explained part in these carbs. The Tomlinson "Dellorto Book" is particularly useless-- it says (basically), "just run 180s, and be happy".
@GomerP, I know there are a lot of voices on the internet, and it's hard to sort the wheat from the chaff-- but I've driven @DannyP's car. The man knows what he's doing. The throttle response and complete lack of a flat spot he's got (at least 50% of which is a result of crank-fire ignition) is astounding. He's going to EFI-- but after driving his car, I don't see the need for it. It was a revelation.
Good explanation of air correction here:
^ That is a great little post, which explains the air-correction jet really well. Something similar on setting float height would square the circle.
I'm convinced that there are only about 10 people alive in the world right now who should be messing with emulsion tubes. 99.999% of us will never, ever get them close enough to warrant changing them.