RPM Drop From Nuetral to Gear
Or move the wires over one spot on the cap.
^^^THIS^^^
How long does that take? 1 minute? Even I, me, the old beat up arthritic guy, can do that in a couple of minutes.
Mechanical advance sticking? Quick way to tell? Easy. Remove the cap and "spring" the rotor against the advance spring, clockwise. it should "snap" back with no delay, nice and free
Vacuum leak? I have no idea.........I'd be checking for that.
Carb float level? Is the carb "puking" fuel, that is visible droplets from the boosters? Usually this results in a "bacon popping sound" as the fuel drops down the carb. Cannot always hear this with a loud engine, or with exhaust leaks. LOOK down the throats when idling
WHAT do the idle screws do? Unscrewing them "more" have any effect? Do they have any effect at all?
Sometimes "really wild cams" do need more air. Holleys generally, have a sort of unobtrusive set screw that effectively adjusts "secondary idle," for lack of a better term. You can set that screw up a little more. to allow some air in the back barrels. This allows the fronts to close back down into the transition slots "Back in" the day, we used to sometimes drill the butterflies
