Yep done this procedure so many times with my vacuum gauges.
But the carbs just don't seem to like me adjusting the air bypass screw. So I end up with them all fully closed.
It's just 1 front barrel with has a slightly stronger vacuum than the others.
When I unscrew the bypass screw just even slightly everything goes unstable.
I've cleaned an replaced the o-rings.
So not sure why. Probably not worth any extra effort as it works good enough. Just wanted them all perfectly matched which is tricky.
The Dellorto 40 DRLAs on my twin cam have the air by-passes. I have them all screwed in hard as I could never get consistant settings with them. Webers don't have and there is no way to adjust slight inbalances on the 2 barrels of one carb.
Personally I would screw yours right in and concentrate on balance across the 2 carbs.
Morgan carbtune is best bet.
You could set the clearance equal from the linkage to the carb, but this is only accurate if the idle position of the 2 carbs is identical.
Before I had the Morgan Carbtune I would do this.
With engine of, wind back idle screws until butterflies are shut. Achieve this just shut state on both carbs.
Now open both idle scres by exaclty the same amount.
Now start car and set idle speed adjusting both sides by the same amount.
Set the throttle linkage clearance exactly the same on both sides
Should be pretty close now. Any better requires some kind on manometer (Morgan Carbtune)