Backfire and Dieseling

[H2O-Z]

Ok, Ive been through most of the previous notes, and am not finding the answer.

I have had the distributor rebuilt, timing set, adjusted carbs, replaced plugs all to no avail.... ('71)

[2ManyZs]

A couple other things to check would be the idle rpm setting and the ignition switch. If the idle is set a little too high this can cause the dieseling. If the ignition switch is going bad it won't cut off the current to the coil properly and this has caused more than one car to run after the switch was turned off. Seems like you have checked most everything, try separating your plug wires, they may be another part of the problem, they could be allowing current to cross over from one wire to the other.