[66StangGuy]

i had the same issue with my holley 600 cfm vac. secondary. heres what happned to me

first the idle speed screw was too high.

i asjusted that so it bairly opned the primary throttle.

then found that the secondaries were sticking open. there is a screw in the back of the carb on the passengers side that adjusts the throttle plates for the secondaries.

then check your float level front and back.

also check the hose that runs from the vaccume source to the secondaries diaphram and spring. there shound be a black hose on the passenger side of the car.

also unplug and cap all vaccume ports to iscolate the problem.
vaccume advance and trans vaccume is not important for idle.