Temperature compensator

In some SU carburetors, a wax-type‘bermostat contained in a housing at the base of the jet head; with increasing temperature, the wax expands and pushes the jet upwards, thereby reducing the effective area of the jet and restoring the correct fuel flow. As underhood temperature increases, fuel viscosity is reduced, resulting in increased fuel flow through the carburetor jet and an air/fuel mixture which is too rich; as this causes excessive emissions, particularly during idling, some SU carburetors feature a capstat temperature compensated jet