Runs worse as it learns....

[steveo]

I strongly suspect my timing match is botched, but I don't know how to fix it.

well you did kinda patch it up by dropping 8 degrees at the distributor. perhaps in that case dropping 8 degrees across the map, putting it back to normal at the distributor, then slowly bringing it back up would be a good starting point...

but without a knock sensor, kinda hard to do any decent knock logging; so perhaps you should consider installing one?