Idling Issues - Holley Carburetor

I have a 340 motor that had an Edelbrock 750 cfm performer carburetor and the car idled at about 900 to 1,000 rpm. I switched it out for a Holley 750 cfm street hp carburetor and am unable to get the car to idle properly. When first installed, the motor started and died within seconds. I adjusted the idle mixture needles which enabled the motor to run without dying. However, I am unable to get the idle speed (with the curb idle speed screw backed all the way out) under 2000 rpm.

Anyone know what the problem could be? Appreciate your input.