In automotive terms, the choke is not what one does to your little brother in the back seat if he has taken favourite toy. A choke or choke valve is something that is sometimes installed in an engine’s carburettor.

The purpose of the choke is to restrict the flow of air so that the fuel-air mixture is made richer when starting the engine (choking in the violent sense involves cutting off air, which is why the name was applied to an air restriction valve in an engine). Depending on the design of the internal combustion engine, the choke valve can be operated either manually or automatically by a temperature-sensitive mechanism; the latter is called an automatic choke. When the engine warms up after starting, the need to apply the choke grows less and less. Eventually, the choke will be switched off when the engine is running hot and the proportion of air to fuel is increased.

Why does a carburettor engine need a choke? It is because the small droplets of fuel do not evaporate well inside a cold engine. If they don’t evaporate, they can’t ignite as well. This leads to that “how-how-how-how-how” sound that you hear from a sulky engine on a cold morning.

If you have an older vehicle with a manual choke, do not forget to turn it off once your car has warmed up, or else you will make the engine run rich, with resulting rough running, petrol fumes and bigger fuel bills.

Fuel injection is now the preferred system inside automobile engines, making the choke obsolete for many modern-day cars. Engine with chokes, however, are still used frequently in motorbikes, propeller-powered aircraft and portable petrol/diesel powered machines such as chainsaws, lawnmowers and line trimmers.
We hope that helps answer the question ‘What is What is a Choke?’!

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