Newold53 there are 2 advances on those distributors. one is external and is the Vacuum advance. The other is Internal (in the dist under the Point or Breaker plate) mechanical advance. The mechanical advance is 2 weights that advance the disty by use of centrifigal force. The faster the dist turns the farther out the weights go advancing the timing. If you have a shop manual there should be a break down of the distributor and you can see the weights that I am talking about. These weights can get gummed up and not work correctly.
