Points and condenser or electronic ignition? I can't remember what year points were replaced by electronic. I found that if a points dizzy is exposed to humidity, the points cam gets a light flash of rust and it become abrasive on the cam follower. As the engine runs, the cam follower wears away closing the points adjustment. Remember that little felt pad in the distributor? Its job was to keep a little lube and rust preventative on the cam. Just a thought and my
Copper