What is a Carburettor?
The old-school mechanical mixer that fed petrol engines before fuel injection took over.
Simplified animation — not to scale.
In plain English
A carburettor (often spelled "carburetor" in American English, and nicknamed a "carb") is a mechanical device that mixes air and petrol in the right ratio before sending the mixture into the engine's cylinders. Carburettors were standard on almost every petrol car until the late 1980s and 1990s, when electronic fuel injection replaced them for better efficiency, lower emissions and easier cold starting. You'll still find them on classic cars, older motorbikes, lawnmowers, chainsaws and small generators.
"Like a perfume atomiser — fast-moving air across a tiny tube draws liquid up and turns it into a fine mist."
How it works
Air is sucked through the carburettor on its way to the engine. Inside, it passes through a narrow section called a venturi — squeezing the air through a tight gap makes it speed up and drop in pressure. That low pressure sucks petrol up out of a small reservoir (the float bowl) through a tiny nozzle called a jet. The fuel atomises into a fine mist, mixes with the air, and the throttle butterfly (controlled by your right foot) decides how much of that mixture reaches the engine. Cold start is handled by a "choke" that temporarily makes the mix richer in fuel.
Signs of trouble
- ⚠Hard starting, especially when cold
- ⚠Engine hesitates, hunts or stalls at idle
- ⚠Black smoke from the exhaust (running too rich)
- ⚠Poor fuel economy
- ⚠Petrol smell around the engine bay
- ⚠Flat spot when accelerating
- ⚠Needs frequent rebuilding or re-tuning
£20 DIY rebuild to £800+ for specialist work on a classic
Always get a written quote. Prices vary by car, region, and parts brand.