Idle Transfer Slot on secondaries?

Nice. This wasn't around in the seventies. I eventually used a finishing nail to create a screwdriver by grinding a flat blade on both ends, phased 90 degrees apart Then I bent it in a "Z" shape to reach up in the screw hole with the carb installed. If you can't engage the slot of the screw, flip it over. Yes, it doesn't take much of a turn. Then go back to the primary idle screw and back it off.. Had a cammed 68 340 Barracuda S with 3.5 inches of vacuum in gear at idle that would burn your eyes out because the power valve opened at 6.5 inches on the Holley 650 double pumper
After a power valve change, a secondary idle stop adjustment, an MSD 6 and with Roads Lifters, I could idle down to 700 RPM..