Carb Issues

[BigSwid79]

I got a mild built chevy 350 with a 600cfm Edelbrock Carb. The engines pushing 325hp and with that carb it shouldn't be too much. I'm getting a rich issue at idle. The carbs loading up and then dogging out if i stomp it off idle. I've somewhat corrected my problem but it still exist. I bumped my timing advance to 40 and left it there. The truck picks up alot better now but I was wondering how to really tune in my Idle Mixture Screws. I want to lean it out a little at idle. I only got 32's on my truck and i should be able to roast them off if my truck didn't dog off the line. I checked for vacuum leaks and that was fine. My plugs were black carbon composite so I know i was running rich. I'm gonna check my plugs in a few days after running with the timing advanced to 40 and see if they clean off any. So please help me on the Idle Mixture Screw deal, if thats my issue? Help!