Carburettor (Carb)

A carburettor, usually shortened to carb, mixes fuel with the air the engine draws in. Air speeds up through a narrow section called the venturi, the pressure drops and fuel is drawn out of the float bowl through calibrated jets. A throttle slide or butterfly controls how much mixture reaches the cylinder.

Most road bikes have switched to fuel injection to meet emission rules, but carburettors are still common on older bikes, small two-strokes, many off-road and pit bikes, scooters and ATVs.

Typical carb problems are a blocked pilot jet after the bike has stood with old fuel, a sticking float or worn diaphragm. Symptoms include hard starting, poor idle and hesitation. For storage, drain the float bowl or use fuel stabiliser, and clean jets with carb cleaner and compressed air rather than wire.