With some of the wonder lumpy camshafts we used to use in the raceboat, the idle quality sucked, they always needed to be 1200-1300 RPM in the water to be reliable, I started (in 1994) drilling small holes in the primary and secondary butterflies (carb had four corner idle screws) to allow the idle air to enter without the butterflies being open, this allowed us to achieve a dead nuts idle at 1000 RPM and the throttle response off idle was astounding. Be careful though, only do this if the butterflies are way open to get it to idle, the camshaft we were using was a mechanical flat tappet that pulled until about 6300 RPM, so this was a radical SOB.
The trick is to start out very small (use number drills) and keep screwing with it until it gets close.
Thats what I did anyway, if the idle mixture screws don't adjust out the mess, there is a chance the butterflies are too far open, after a certain throttle position the idle circuit gets taken out of the game.
