dunlop01:
It is an air flow number for the Simmons Carb Comparator. The Simmons simply "compared" one carb to another. A 9.1, if compared to a pretty good carb is actually very good. However, if 9.1 is compared to a stock, never reamed carb (if memory serves me, such a carb would be in the 7.8-8.1 range) it would not be nearly as good. It is simply air through the air horn and bore and is not a measurement of fuel flow. CMac