Edelbrock 600 carb issue?

Ignition tune-up (cap/rotor/plugs/wires) made no change. Called Edelbrock tech and they were not much help although nice enough. Their only recommendation was to put some fuel system cleaner in the tank and see if that helped. I guess I will try that although it sounds like a shot in the dark. Next step I suppose will be to try changing the step-up springs to a lighter spring and see what that does. Tech recommended the orange or pink springs (5 and 7) respectively since the car motor pulls 13-15" of vacuum at idle depending on the mixture adjustment. Idle mixture has seemingly no effect on the problem though. After re-reading the edelbrock manual, I'm thinking that the problem lies somewhere in the transition from the idle system to the primary metering system. Any thoughts??
Thanks,
-Tim