Hmmm...it's going to change according to your idle speed. The main thing is to make sure they're all the same. On my twins, there's one carb that's not adjustable, and you use the other's concentric adjusting nut to match it. Get them the same, and you should be good to go.
I use a flexible measuring tool from a carb rebuild kit for a Qjet carb, it goes down to 1/64's if you can see the marks. Just make sure they're all the same, and keep your idle within stock specs, too high and it won't want to start.
