Jet (Carburettor Jet)

A jet is a small brass part with a precisely sized hole that controls fuel flow in a carburettor. The number stamped on it indicates the flow size; a larger number means more fuel. Most motorcycle carburettors have at least a pilot (slow) jet for idle and small throttle openings and a main jet for wide-open throttle, with the needle and needle jet covering the middle range.

Changing jets, known as jetting, adjusts the mixture for an exhaust or air filter change, altitude or temperature. Too small a jet makes the engine run lean and hot; too big makes it rich and sluggish.

Pilot jets have tiny holes that block easily when fuel is left in the carb over winter. Drain the float bowl or use a fuel stabiliser before storage.