I just had my 350 engine rebuild and it includes a 600cfm edelbrock 4bbl carb. I was tuning it a bit and jets are fine and gasket came with carb and fits the manifold well. This car is not vacuum advanced. The idle screw (left screw facing car) works fine as i did the bog test and did my recommended turn(s). The mixing screw on right does absolutely nothing,i can unwind and wind it both ways as far as it goes and nothing. The plugged vacuum holes under the screws have suction. I am stumped on this. Is this a defect or my error?

 

Doesn't sound like anything you did wrong. If one works properly and the other one has no effect that's almost certainly either debris inside the carb or something wrong in it's manufacture.