Kind of a new one for me..... any ideas ???

Lets get right to the details. '74 Duster. Was slant, now 318. It did this with the slant and the 318.

• IF I let the car sit for a period of time (two weeks to a month??), it will turn over great by the key but no spark. I've replaced ballast, ecu (and grounded well), coil. That little "starter red button" deal that the '74's have is bypassed.
• To start it right up, I run a jumper wire from the +coil to +battery. It pops right off and runs great. Then I remove the jumper wire right away with it idling and then the issue is gone. It will start every time with the key as long as you at least drive it once a week.
• Any ideas? (besides start it every 3 days...LOL) thanks