What is a choke for and how does it work, on small engines.
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When you are starting an engine cold (as in at environmental temperature – in this context 30°C / 86°F would be considered cold – operating temperature for my engine is 80°C /176°F) you have to use a fuel rich mixture to effectively move the cold, unlubricated pistons resulting in additional heat to warm the engine up and get the oil to operating temperature. The choke is the mechanism which controls the air-fuel mix. The same thing occurs with fuel injected vehicles only you have the car’s brain (ECU) doing it for you.
Watch a car when it starts up cold and idles for a bit – particularly ones with a big engine capacity (3l, etc.) – you’ll see water pouring out of the exhaust. This is because water is a byproduct of gasoline/petrol/diesel combustion and the fuel/air mix at startup is so rich that the excess water vapor condenses in the cold tailpipe/exhaust.
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