what size carb for a 416 stroker

Currently running a holley avenger 770. Holley website says I should be running an 870 cfm carb on a mild 416 stroker motor. My issue is that at idle my car seems to be running real rich when I smell the eye burning exhaust. Once I am underway it seems to clean itself up. I was thinking that maybe the 770 is not providing enough air flow at idle which is causing it to run rich. I have edelbrock aluminum heads with a performer airgap intake.