Carters have transfer slots just like Holleys, I think it's a necessity in pretty much any fixed-venturi carb...?
If you had a dual-plane intake with the same problem (carb too rich on one side) it would show on cylinders 1, 4, 6 & 7 or 2, 3, 5 & 8 because the plenum and runners are split to create even intake pulses based off the firing order of a V8.
See if it'll take more initial timing, what kind of vacuum is the engine pulling at idle now? Also might want to check valve lash just to rule that out.