That carb appears from the pictures to have:
(2) idle mixture control screws
(1) idle air bleed screw (the one in the center)
(1) fast idle screw (the one on the linkage)
There is no curb idle screw. The screw on the linkage should only be used to control the fast idle (engine cold) RPM.
Without knowing exactly what carburetor you have:
Many of the Pontiac AFB's with no curb idle screw had suggested INITIALsettings (engine at operating temperature) as follows:
Idle mixture control screws at 1 turn (2 1/2 turns is the maximum) (with the RAIII cam, I would suggest 1 1/2 turns starting point)
Idle air bleed screw at 1 1/2 turns
From there, as Sirrotica posted above, it is trial and error
Something to try would be run the engine at a fast idle, maybe 2500 RPM, then manually close the choke butterfly. The engine should slow. Release the choke before the engine stalls. If there is crud in the idle circuit, this will sometimes clear it.
Jon
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"Good carburetion is fuelish hot air". 
"The most expensive carburetor is the wrong one given to you by your neighbor".
If you truly believe that "one size fits all" try walking a mile in your spouse's shoes!
Owner of The Carburetor Shop, LLC (of Missouri).
Current caretaker of the remains of Stromberg Caburetor, and custodian of the existing Carter and Kingston carburetor drawings.
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