Some say it was a Very small gain in performance to vary the plug ranges(ex 1,6 had the same 2,5 had the same & 3,4 had the same ) Being 3 different heat ranges due to how the fuel was being distributed to those cyl. There could? be some other issue at play here But with out seeing the Plugs or hearing the motor. Carb could be in need of tuning(floats air fuel mix etc), timing ajusted how and where the PVC is setup,a small vacum leak ? I personaly never had that issue on my Offey (600 holley). I never ran a single 4bbl cifford Only my dual(450s) and My own 3x4 tunnle ram.(again 450s)
God doesn't like ugly.
