Everyday Performance LLC has produced a limited run of the 1966 Buick Qjet Fast idle cam. The originals (#7031155) are frequently found cracked and/or broken from heat and age. Replace that worn original with a new reproduction from Everyday Performance LLC! $35 shipped for V8buick members or you can buy it as a set with the 1966 Buick Qjet pulloff actuator! $60 shipped for v8Buick members
Picked up both these parts a few days ago - great quality, fit like a glove and totally makes these carbs usable again. Also fits the more common 7041304/306 service replacement carbs.
Number 15 is the fast idle cam on that diagram, however that diagram is of a newer model that has a metal cam. Early carbs 1966-1969 used plastic fast idle cams which are frequently found cracked or worn these days. So on a 1966 buick qjet, the idle cam is in the same position as shown in your diagram. The pull off actuator, not shown in your diagram, resides inside and under the forward metal cover on the passenger side of the carb.