That problem sounds like you are not maintaining the power to the ign coil during the cranking phase.
Put your meter on the +side of the coil and see if you are getting near 12 volts
when your cranking the engine over with the key switch.
Also:
A weak bat-tree might be producing enough power for the starter, but not enough for the coil.
your wiring circuit is a simple one, not complex like some later models, so you should be able to find your problems easily.
