[Spyglass]

Originally Posted by spdbrake

Curious if you have vac advance on your distributor?
You mentioned easing into the throttle (vac advance would be pulling max advance still) and it runs fine.
Then you mentioned when throttle up aggressively you get the misfire (vac advance will not be helping the the timing will be retarded quite a bit).

You may have phasing issue in the dizzy where your too much advance or too much timing retard (your rotor is in between spark plug posts). This is a problem more common on small diameter distributors and can cause scatter and crossfire.

https://www.youtube.com/watch?v=aWMlNwGW0tM

Bad phasing and crossfire
https://www.youtube.com/watch?v=zulDzQ5q9TM

Everything You Wanted to Know About Vacuum Advance and Ignition Timing

Good info, thanks. Not sure whether I have a vacuum advance on the distributor, I'll check. Since the issue may now have moved to the dreaded intermittent category, this may not be the issue. Appreciate your input.