Variable jet - SU type- Piston chamber Piston Throttle Main jet Jet needle Choke adjustment to jet Fuel pipe to jet Float chamber Float Float needle Fuel feed pipe stub

The SU is the simplest type of variable jet carburettor, the other main type, the Stromberg, has a rubber diaphragm instead of a piston.

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How variable-jet carburettors work

A carburettor mixes fuel and air in the proportions and quantity the engine needs at any time. I...