[old ugly]

any of these things might be a little worn. the timing gears, the center cam gear that drives the distributor shaft, the flats on the distributor shaft, and the drive that rides on the cam. lots of places that wear can exist. all those spots can do that.
if that dist drive that you have the screw driver in feels fairly tight put it back together.
grab the rotor and see how much twist is there.
if that is minimal
re-time it as per the service manual.
make sure the points are cleaned and making contact , test light. your 12volt light ,if it is not LED, will work on the 6 volt system.
you need to time it with a test light or ohm meter as per the book.
make sure it has compression, fuel, timed and spark that is what it needs to run.