choke

In an internal combustion engine, a choke valve modifies the air pressure in the intake manifold, thereby altering the ratio of fuel and air quantity entering the engine. Choke valves are generally used in naturally aspirated engines with carburetors to supply a richer fuel mixture when starting the engine. Most choke valves in engines are butterfly valves mounted in the manifold upstream from the carburetor jet to produce a higher partial vacuum, which increases the fuel draw.
In heavy industrial or fluid engineering contexts, a choke valve is a particular design of valve with a solid cylinder placed inside another slotted cylinder.

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