It has been supplied in both 1 ¼ and 1 ½ inch S.A.E. flange sizes. Five conventional circuits are used. They are:
All BBD carburetors prior to 1974 are of the air-bled design incorporating downhill nozzles. 1974 and later models are of solid fuel design with uphill nozzles. The solid-fuel design provides more precise fuel metering to meet emission standards while still maintaining maximum response and drivability. For increased life and smooth operation, the solid fuel design uses a Teflon-coated throttle shaft.
All fuel enters through the fuel inlet fitting in the bowl. The fuel inlet needle seats directly in this brass fitting and is controlled by the twin or dual floats which are hinged by a float fulcrum pin. The fulcrum pin is held in position by the “horseshoe” retainer. The twin floats follow the contours of the fuel bowl and are designed to provide a stable fuel supply under all conditions. Only a minimum of fuel is maintained in the carburetor, preventing excessive fuel evaporation. This tends to improve warm engine starts.
The float circuit must constantly maintain the specified fuel level as the other circuits are calibrated to deliver the proper mixture only when the fuel is at this specified level. When the fuel level in the bowl drops, the float also drops permitting additional fuel to flow past the inlet needle into the bowl.
The bowl is vented to the inside of the air horn. The bowl vent is calibrated to provide proper air pressure above the fuel at all times. To assure a positive seal, always use a new bowl cover gasket when reassembling. An air leak at this point can result in a mileage complaint.
Remove float to adjust. NOTE: To obtain his proper alignment it may be necessary to bend the float lip at either or both arrows “A” and “B”. CAUTION: Never allow the needle to be pressed into the seat when making the adjustment as this might damage the viton tip.