I think I need to explain distributor function traditional type ignition.
In the body of the distributor, attached to the shaft, are some weights and springs. The function of the weights and springs is to advance the ignition with revs and the springs to return the timing to the static figure when the engine slows down and stops.
On road car distributors, there is also a vacuum can which is aimed at putting more advance in when the inlet vacuum is high. An example of this would be accelerating to cruising speed. While accelerating, the can does nothing, but when cruising speed is reached, the driver lifts off the throttle, a high vaucuum is formed in the inlet manifold and the can further advances the ignition on what the weights have done. You don't need or get extra power, but you gain in fuel economy. Put your foot down to overtake, the vacuum disappears, the ignition goes back to the weight only setting so you lose the extra advance. This is fine as the weights and springs give the advance for load, and the vacuum can only the further advance for economy.
No where though does the distributor retard timing, it advances the timing with revs, and it advances the timing with vacuum.
If the balance weights stick, the most common symptom is the timing remaining advanced as you slow down, and if you then press the throttle, the car 'pinks' but doesn't do it from rest. Cure is usually as simple as a spray of light oil on the weight mechanism.
Calling the vacuum can an advance and retard device as many do distracts from its real purpose, an economy device.
Although a good explanation, i think a little complex for some one who doesn't even know where the "CAN" is, also you have not mentioned about actually setting the Ignition timing from the body of the distributor with strobe over Crank wheel, this would be necessary to evaluate whether the ignition timing is advanced or retarded, now this even confuses the situation more as you Quote, "no way can you retard the timing you can only advance" when we used to service a vehicle, the Distributor Advance "CAN" as you say, would be checked and freed off, ie by squirt of WD and a little light oil, once it is proved the mechanism is working, then the Timing would have to be set, a little more complex than a Mechanic showing you in 5mins, I THINK
