2 bbl carb

There is/are a few ways to get to the same place. I chose this way cuz its fast, easy, and right on. The engine dictates it's own idle timing, based on the carb being used and where it's transfer slots begin.
The goal is for the engine to not have a tip-in hesitation, that is all. Using the mixture screws as trimmers you can get the engine to idle almost anywhere on the transfer slots.
But if the throttles are too low, then the transfers run the risk of drying up, and so when you tip the throttles in, she goes lean and probably stalls. As you increase the T-slot exposure, the tip-in progresses to a hesitation, a sag, and finally smooths out, then richer to where the mixture screws have to be closed up and then just plain fat at idle, going lean at tip-in cuz the screws have been shut off.
Starting with the T-slot exposure being square, and mixture screws a lil fat, takes most of the guess work out of getting the tip-in sag gone. But that just leaves the timing to set the speed with. And since the engine will idle on just about any idle-timing, the difference being mostly just speed, it's a natural.