My guess is, its more of a carburetor issue than electrical if the car has no starting issues.
so the possibilities are
1. week plunger valve, seal in the carburator.
2. bad mixture
3. loose throttle body (Butterfly)
4. leaked vacuum pipes
5. pipe to the vacuum advancer is absent/leaked.
6. vacuum advancer diaphragm is not working
to check (No.6) remove the distributor cap, and disconnect the pipe from the carburetor side. suck air from it and you should see the lower coil assembly inside the distributor move slightly clockwise. if you can suck air in without any resistance then replace the distributor advancer (estimated cost 500).