SU Carburetters

If an insensitive Harley rider very quickly opens the throttle, the air flow in the carburetor can collapse. Fuel is then no longer delivered to the jets and the mixture becomes lean. The solution to the problem is to install two throttles in the carburetor: one, the throttle disc, is controlled by the throttle grip via Bowden cables, the second, a slide valve, is controlled by the intake vacuum. In the SU carburetors, the slide is attached to a piston that slides up and down in a dome. (The other equal pressure carburetor on Harleys, the Keihin CV, has only a rubber diaphragm under a flat cover instead of a piston and dome). You can therefore recognize the SU-type vacuum carburettors by this voluminous bell above the actual housing.

SU carburetors have been a good way of breathing more life into a Harley-Davidson V-engine since the 1970s. Skinner-Union (S.U.) carburetors have been found on various English automobiles since the 1930s, from Morris to Jaguar. Legend has it that they were first flanged to a Harley-Davidson engine by a certain Mel Magnet (yes, that's right: the founder of Rivera Engineering). He was immediately crowned "King of Carbs" by Custom Chopper Magazine. These legendary carburetors have been in production again since 2023 and we immediately got hold of some to present them here. We also offer a selection of replacement gaskets and accessories.