Holley Street Avenger 570 Idling Problems

I've been running this carb on my Cuda for a while with no problems.
Recently installed a fresh rebuilt 68 model 318 engine with this carb, a new Weind aluminum intake to replace the stock , cast iron 340 intake and a Mild Comp Cam and lifter set ( 455 lift, 268 duration). Also installed an electronic distributor.
Vacuum is 14-15 at idle warmed up, timing is at 14 initial, 35 total. Will idle good in gear only after fully warmed up ( stock converter ). Otherwise, I have feather the throttle while putting it in gear, then if it doesn't stall it's OK.
Talked to Holley, they suggested cracking open the secondaries to help close the primaries at idle, to better allow the idle mix screws to work. This helped, but the problem is still there.
Started off running the factory recommended 54 jets in the primaries. Tried jumping up to 56 primaries, helped a little but the plugs are showing some black.
Have been checking for vacuuum leaks, but have found no evidence.
Any suggestions would be appreciated. Larry