[Ross F-1]

Ditto the comments on idle below 13:1, but that is also with a carb, where the idle system is in play for a good bit above idle.

I'm running an MSD ready-to-run distributor with manifold vacuum to the advance, using a specific GM advance unit that limits vac advance to ~8 deg. Very hard to get a smooth idle with that much advance and lean idle mix.

I would point out that the Innovate O2's are not super accurate, in my experience. I've had two of them and the latest one reads almost a point (1.0) lower (richer) than the other one did, with no other changes.