They are called idle mixture screws because they adjust your carbs only when running on the idle circuits, once your primaries trip in they won't have much effect on anything. Drop your hot idle down to around 750-800 and you should be able to adjust your idle mixture. To set a baseline turn them all the way in (gently) til they stop, then back out 11/2 turns each. That should put you in the ball park to start fine tuning.

*Use caution leaning the outboards, you can melt pistons if they are set too lean, that's one reason the factory sets them and plugs them with lead so people don't accidentally burn up thier engines tinkering.