On Carter/Eddie carbs, no provision to idle up the secondaries. Is static/ initial timing set correctly? Have a PCV connected? You can drill small holes in the butterfly valves to get higher idle and still keep Idle mixture screws functional.
Timing was chosen when the engine was on the dyno for break in. 18 initial and 34 total. I've since switched carbs and been working with this one. I am running a PCV. The idle mixture screws do have some affect on the rpm but the car will just chug along even with them closed (one at a time). I assume I should have the t-slot squared off properly correct? Then like you stated drill small holes in the butterflies? Also by small are we talking 1/16" and maybe a couple or just one hole in each primary butterfly and increase the hole size for desired idle??