New jets are in. Larger idles and larger pump jets.
She will tickover now without choke. Choke on kills the engine once warm.
Steady opening throttle revs fine
Sudden opening throttle spits and backfires
Idle mixture screws have no effect
Idle is not steady. It picks up and drops periodically.
Butterflies are as closed as they physically can be
So... Getting somewhere at least. I think a stronger spring in the accelerator pump will help squirt fuel faster, still not enough fuel when opening the throttle quickly.
I think that it is either idling on progression somehow, or there's a vac leak somewhere, or both.