I had a similar issue with my 85 Series III these are the steps that I took to resolve the issue.
- pulled the plugs and inspected the burn. which looked fine
- performed a compression test with the throttle body open all the way, and air filter off all cyl were at 145psi
- Inspected the cap and rotor - it looked like it had recently renewed
- checked the timing as best I could with an engine that wouldn’t run
- checked the resistance of the spark plug wires - checked out just fine
- Went to HF and picked up a lighted spark lead. Installed between plug and the HT lead spark was intermittent.
- checked the output in and out of the ignition module. checked out.
- Checked the output on the coil. Bingo! I picked up a Mallory HE coil with an internal ballast.
Fired right up. real good burn on the plug, and an impressive acceleration.