Automatic stalls in reverse.

I always advance timing for highest idle; but at the far retard end of that range. You can move the distributor a little and the idle will not change much from that high point. Try it with the vacuum advance hooked up and also with it disconnected. More importantly; with the vacuum hooked to a full vacuum source and try with a ported vacuum source. So, that's three different ways to try it; giving you three different throttle responses.