so we hook the timing light up and the vacuum gauge to a non ported manifold vacuum off the base of the 4160 carb and the needle won't sit still, it jumps spastically between 15 and 20 PSI, see video
we bottom out the idle mixture screws one on each side of this carb (it only has two) and then turn them out 1.5 turns as per Holley's instructions
than we play with them screwing them all the way in slowly then backing them out to about 2.5 turns, and that pesky needle keeps dancing and won't stabalize
https://www.youtube.com/watch?v=ry9ShldWpUg