Choke valve

A choke (also choke [ t͡ʃoʊk ] ) is a component for carburettor engines, which allows a specific limitation of the incoming air in the carburetor.

Because a large portion of the insert in the intake air fuel translates into a cold engine in the intake manifold and on the cylinder wall, is increased during cold start the fuel content in the mixture. One speaks of enrichment or enrichment of the mixture.

Achieved is through a further limitation of the air entering the carburetor air using an adjustable choke. This is in front of the nozzles usually right on top of the carburetor and has one or two notches on the edge. As is the fuel outlet opening of the main jet between the starter valve and the throttle valve, to flow easily due to the increased negative pressure upstream of the throttle bit more fuel into the air stream. Considered Figuratively constricted to the engine with this flap, the air supply partly from, hence the English name Choke ( t͡ʃoʊk of Engl. Choke to choke, strangle ).

There are manual, semi-automatic and automatic versions of the choke.

Manual choke

When manual choke the choke is operated ( here exemplarily for a car) on a button in the vehicle via Bowden cable by hand. Before starting operation, the button is fully pull out, then the engine is started, and pushed back after a short warm-up phase of the button. This design was until the early 1980s standard for carburetors of cars and motorcycles. The fact that the driver was responsible for the operation, resulted in practice often a too high fuel consumption, because the choke was often operated for too long or was not opened again properly in extreme cases. Today, this arrangement is mainly used in two- and four-stroke power equipment such as chain saw, lawn mower etc.. Also in small aircraft is usually still a manual choke available. In many of today's lawnmower engines can be found instead of a separate choke control a lever design that closes the choke if the gas lever is moved to the maximum position, and automatically opens it again when restoring rules.

Semi-automatic choke lever ( automatic start )

In a semi-automatic choke flap with the accelerator pedal and a bimetallic spring is coupled. Before the start of the accelerator pedal is fully durchzutreten once to activate the choke. Subsequently, the engine is started. After the warm-up phase of the choke is automatically disabled by the expanding bimetal spring. Semi-automatic chokes were common in the 1970s and 80s.

There versions electrically heated bimetal, for example, air-cooled engines VW. This incorrect operation of the choke by the driver was largely excluded.

Fully automatic choke

The fully automatic choke is used in modern carburetors and has the original choke only the name in common. It is a system of diaphragm pumps, electric pre-heater and bi-metal strip.

For engines with fuel injection there is no such more flap mixture enrichment is carried out, inter alia, increased injection volumes.