Ok hang on, I musthave got my wires crossed. In though you had installed a Carter type carb.
With a Holley type carb, and the 6900 cam, the Mixture screw adjustment should be ~3/4 turn out.
But I'll say it again; MAKE SURE the choke is OFF and is NOT interfering with the curb-idle screw.
The Transfer slot is your main low-throttle-opening fuel circuit. At idle, with the secondaries closed tight You have to have a slot exposure AT BLEAST square, as said before, AND you have to add a lil from the mixture screws just enough to smooth the idle.
Theoretically, you can idle the engine on one or the other circuit. But, the carb will not function correctly either way; it must have enough transfer fuel to not have a tip-in hesitation, as you have found out.
Otherwise all that I said is the same.