HEI's are notorious for their mechanical advances to stick or completely freeze up on the shaft over the years. It may be time to pull the distributor and have it rebuilt professionally. We did thousands of them over the years for racing and street performance guys and always had to tear them down completely and polish the distributor shafts and de-gunk the advance plate to remove years of varnish and other stuff to free them up. Once you do this, it will be good to go from now on.
