Six4me - when running multiple carbs, the design of the intake has much to do with the total CFM of the system; but under best case, the total CFM of the system will be less than the sum of the CFM of the carbs. There is no "ballpark average" in this area.

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop