340 Edelbrock Carb Adjustment
stay with the edelbrock
the idle screws have nothing to do with anything but idle fuel metering
sounds like a needle or jet swap down a size or 2...buy a kit and drop it down until it doesnt do it anymore...a better indication would be to check the plug colour
I run a 625cfm on a 400hp 340...all a bigger carb is going to do is cost you more $