Re: need help with this
Just from your description, it sounds like the secondary carb plates are cracked open. I'm assuming it's a Holley, since you mention 4-corner idle adjustment screws. There may be other carbs with 4-corner adjustment, so please nobody bite my head off.
Anyway, there is an adjustment screw that will allow the secondary plates to close all the way. I would start there. Your adjustment at idle should come mostly from the primary. I would check the carb manufacturer's web site and get instructions on setting the primary and secondary butterflies.
Also, an easy test would be to swap out another carb from a buddie's car; one that you know is running properly. That way, you could see if the carb is actually the problem. You could have any one (or more) of a number of other issues; vacuum leak, bad cap, rotor, wires, coil, etc, etc..........
Dave F. in Rhode Island
'68 Camaro SS Accel DFI 454 (SOLD - I'm a boring Corvette owner now)
Bought my first big-block Chevy in 1970