Tom you may be running them but according to the ages old cfm formula you are over carbureted. The formula is (rpmXcu.in.Xvolumetric efficiency)/3456. Thus a 428 spinning 6k operating at 100% volumetric efficiency (which no or very few engines do) requires only 743 cfm. Two 750s fully open would be more than that probably?. The old bathtub LeMans sd cars ran two 750 cfm carbs on 421s and they too were probably slightly over carbureted. Of course I know your 428 is in a street car with progressive linkage and you are thus running off of the front two barrels of your rear carb almost all of the time so no harm no foul.
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