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Keihin 40mm "Butterfly"type Carburetor.
A keihin v571d5
A 2002 Sportster has a Keihin Constant Velocity (CV) carburetor, 40mm.
36mm Keihin PWK
The 1983 FXSB came stock with a Keihin B28E 38mm butterfly-type carburetor. First use of the Keihin CV carb was in '89 for Sportsters and '90 for all big-twins.
The OEM carburetor for a 1979 FLH-80 is a Keihin B78B butterfly type.
The 1983 FXSB came stock with a Keihin B28E 38mm carb, which is a butterfly-type, that is to say a non-CV (constant velocity) type. CV Keihins didn't appear until 1988.
Keihin Corporation was created on 1956-12-19.
42 pilot 150 main for stock Keihin butterfly carb.
Normally there is a metal tag attached with the Model # of the carburetor printed on it. It may or may not have the part #. The part # is usually stamped into the carb somewhere. Look everywhere especially on the base. Once you find the model # there are web sites that will identify what carb you have.
On most if not all 2-barrel and 4-barrel carburetors the part number is located on the front left (driver's)side of the air horn.
Champion Carburetor buy's carburetor cores. Their number is 1-855-832-6743.