There is a number of possibilities could be to large of an air gap between the signal rotor and pickup midule in the distributor,it should have an air gap of.031 in.
There could be an open or short in the primary or secondary windings in the coil: remove the coil and ohm the primary and secondary windings: the primary should be 1.08-1.32 ohms between the positive and negative control wires.
The secondary resistance should be: 22.1-29.9 Kilo ohms between the negative control wire and the spark output terminal(the coil plug wire tower that goes from the coil to the distributor).....
Check to make sure you have a good ground connection from the coil negative to ground.