idle with the throttles closed
Well, they never completely close.
The idle mixture screws will only be the same number of turns if the carburetors are exactly alike (including throttle shaft leakage, float level). Better to get each one to idle best separately, then use the Uni (or whatever) to set the idle speeds to match.
The speed matching above idle is done with the linkage; the arms must be the same length (throttle shaft to link hole), and be at the same angle with no slack.
Yes, you have to go back and do the mixture again if the speed changes by more than a little.
Important: if the ignition isn't correctly set, you're wasting your time - this must be done first.
