A power valve opening at idle will not cause rich idle.

I'm with 1 Wild R/T in that you need to check t-slot/throttle plate relationship. Drill holes in the throttle plates only as a last resort, after you're sure the timing is where you want it, etc.

Do a search for 68Bullit's post entitled "Holley Rich Idle" or something similar. He had a situation similar to yours and the transfer slot thing is discussed in detail.

What is this carb - a 3310, double pumper...?

Jim