here is a clip from the site below.
According to the Weber operation manual, proper throttle valve position at idle should block the first progression hole with the bottom edge of the throttle plate aligned to be level with the bottom of the first progression hole. On a new 40mm Weber this would correspond to an idle stop screw adjustment of about 1/2 turn from throttle plates completely closed upon the ID of the 40mm bores in the throttle bodies. This is a physical setting that is not to be adjusted.
Tuning the Weber Carbs
this opened my eyes to carbs. i wish i had read this when i had webers.