another thing to try is inserting a piece of wire into the idle air bleeds to restrict the holes there , this often Cures low vacuum stalling issues . think of the 6 pack as a 4 bbl the cenrer carb does most of the work the secondaries are just along for the ride . there are idle mix screws in the base of the outboard carbs though often hidden behind steel plugs , I go underneath & drill a small hole from an angle & pop out the plugs to access the idle mix screws , the rear carb I base line about 1/2 turn out from the bottom , once it is in place it is very difficult to adjust ,the front is easy though .
