Venturi sleeves (24, 26, 28 and 30) are telescopically moved upwardly into the bores (14, 16, 18 and 20) of the carburetor body (12) until the annular shoulder (46) of each sleeve abuts a corresponding shoulder (36) of each bore. Booster venturis (74, 76, 78 and 80) are suspended coaxially with respect to the venturi sleeves (24-30) with the support conduit (86) extending through a notch (52) at the first edge of the venturi sleeve. Positioning cords (50) are formed in the lower outer cylindrical surface (44) of each venturi sleeve (24), so that the positioning cords (50) must face and abut each other when the venturi sleeves are properly inserted into the bores of the carburetor body, thus assuring that the sleeves are properly oriented in the carburetor body. Flow director surfaces (104, 106, 108 and 110) in the carburetor bowl (102) guide the air toward the venturi sleeves.