I am trying again. Do you time a GMC or any chevy of 1941 era with the vacuum advance connect or disconnected to the distributor ? The engine is timed fairly well but when you hit the throttle it advances very quickly and will back off, when you release, but not totally. There is nothing wrong with throttle setup on the Zenith. Suggestions please or comments. Thanks Doug P.S. I timed it without the vacuum connected.