It is not normal for the cruise AFR to bounce around so much. Fuel is being pulled (or leaking) from somewhere it should not be coming from under cruise conditions.

Is this a "Mighty Demon" carb? Have you looked at the metering blocks to determine if the Idle Feed Restriction (IFR) is removable (ie a jet with threads)? Are the Power Valve Channel Restrictions (PVCRs) removable?

Do you know the history of the carb? Are all of the gaskets in good condition?