I have a 1969 chevelle with a 250ci, how many c.f.m. is the stock single barrel carb?
If you'll measure it, then you'll cut through any variables and anomalies that are possible.
1-7/16" throttle bore, 1-7/32" venturi = 160 CFM
1-11/16" throttle bore, 1-5/16" venturi = 210 CFM
1-11/16" throttle bore, 1-1/2" venturi = 250 CFM
Keep in mind, that since these are one barrel carbs, that they are rated at 3 in.Hg pressure drop and not at 1.5 in.Hg like all 4 bbl. so you must multiply the above ratings by 0.7072 to get them in "4bbl. speak" if comparisons to 4bbls are to be made.