[FED 387]

Not sure of the carb specs that is being used with that particular combo but the smallest AFB is rated @400 CFM and they go up in size to 750 CFM while a WCFB is kinda rated @ 385 CFM for the smallest ones--- Found this a long time ago not sure how accurate it still is

AFB Carbs
CFM Venturi Diameter Bore Diameter
Primary Secondary Primary Secondary

400 1 1/8 1 1/4 1 7/16 1 7/16

500 1 3/16 1 1/4 1 7/16 1 11/16

575 1 1/4 1 9/16 1 9/16 1 11/16

625 1 3/16 1 9/16 1 7/16 1 11/16

750 1 7/16 1 9/16 1 11/16 1 11/16

ALL AVS CARBS

Primary & Secondary same size 750 CFM
Primary & Secondary different size 630 CFM

4GC CARBS

CFM Venturi Diameter Bore Diameter
Primary Secondary Primary Secondary

486 1 1/8 1 1/4 1 7/16 1 7/16

553 1 1/8 1 15/32 1 7/16 1 11/16

692 1 1/8 1 15/32 1 9/16 1 11/16