If you truly mean that they are seated then you have to be getting fuel from a transcition circuit or the main metering circuit due to the throttle blades being open past the idle slot, or a very high fuel level setting. If you do have about .020" of the idle slot below the throttle blades, then I would need more information. The idle air bleeds getting larger will make it leaner if they are air bleeds for the circuit and not air by pass bleeds?
On my holley carbs with changeable air bleeds typically will need about 3/4 turn off the seat when adjusted for best vacuum on all 4 corners. I have only had a few bone stock marine holleys like the 1 1/2 to 2 turns out and they were not adjustable in any other way other than the idle mixture screws.
Are the screws all the way in to the seat or are they just at 5/8 to 3/4 turn out?
Bruce