SU carburettor, 1965.
© Science Museum / Science & Society Picture Library
Sectioned. The carburettor is the component in an internal combustion engine which mixes air and fuel in correct proportions for combustion to occur. The SU (Skinners Union) carburettor is a variable choke carburettor invented by the Skinner brothers and originally patented in 1905. It was designed to automatically give the correct mixture under all conditions of running. It operates by maintaining a constant velocity of the air past the petrol jet, the air pasage and the jet orifice being automatically varied in correct proportions according to the demands of the engine.