Check the voltage at the coil + terminal during cranking. If it's less than 4.5V from a 6V battery, find and fix the high resistance between the battery and the coil. Look for loose, dirty primary wire connections, and/or dirty contacts in the ignition switch. Never,- - - - -ever, run a resistor on a 6V coil- - - -internal or external.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!