Dieseling is caused by the engine idleing too fast (throttle open too far). Advance the timing, then adjust the idle mixture screw for the best (smoothest) idle, then set the idle rpm lower.
The distributor mechanical advance, vacuum advance and carb idle adjustments respond together and any one of them can effect the idle and throttle response. Sometimes you have to modify one, or all, of them to get it to run right.
Ron
