If you are still sorta OEM
You have a "Prestolite" distributor and ignition system.
(not ruling out other stuff)
That is, the distributor has a white plastic front with two cylinder looking things, one of which has a vacuum port for the vacuum advance.
Just from experience, Prestolite is not great, I upgraded my 1977 to Motorcraft, found in the 1979's
Lets do a little test!
Hook up the timing light
Plug the vacuum advance hose that feeds the distributor.
Fire it up
See the harmonic balancer mark-steady on the timing numbers (as in the link I gave you)
Increase the engine speed
Is the mark moving (advancing) or not?
Return with results!
Images (Click to enlarge)
Thursday, June 23rd, 2016 AT 3:57 PM