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Keihin carburetors are used on almost all Honda motorcycles (or copies of Hondas). Here we focus on the 50cc moped, mini-cycle and scooter carburetors mostly from the 1970’s and 1980’s.
From Wikipedia: The Keihin Corporation was founded December 19, 1956 and currently maintains its head office in Shinjuku Ward, Tokyo, Japan. Among the products they are internationally known for is the production of carburetors and fuel injection, and is a major suppler to Honda, and also Triumph, Suzuki, Kawasaki, KTM and Harley Davidson motorcycles. In addition to carburetors, Keihin supplies the automotive industry with engine, transmission and climate control products, including intake manifold assemblies, HVAC assemblies, compressors, valves, solenoids and electronic control units. Keihin’s largest shareholder is Honda Motor Co. Ltd. Keihin first began U.S. manufacturing in 1989. Counting all U.S. locations, Keihin has more than 20,000 employees. Keihin North America’s corporate headquarters is in Anderson, Indiana.
Keihin motorcycle carburetors are labeled with a cast-in model ID prefix followed by several numbers and letters that specify the carburetor version for that application. Most of these Honda moped, noped, mini-cycle, scooter and small motorcycle carbs are Keihin prefix “PA”. Other Keihin motorcycle carburetor model codes are PB, PC, PD, PJ, PWK, CV, CVK, VB, VD, VE.
Flange mount: The Keihin PA family of carburetors are flange mount. Flange mount carbs have a diamond shape mounting flange with bolts on either side of the main air hole. The bolt holes can have different spacing.
Carburetor replacement: When replacing a carburetor the new carb must have the same bolt hole spacing. There is a way to get around this by making the bolt holes into slots. With slotted mount holes the flange mount carb is not automatically centered, so it has to be manually positioned in the center as the mount bolts are tightened.