What is a Choke Valve in the Carburetor?

A choke valve is an important component in a carburetor. The choke valve is usually a butterfly valve located at the entrance to the carburetor. The choke valve is usually used in the carburetor to give the engine a warm start in cold weather. 

In this article, I will discuss what is a choke valve in the carburetor? 
What is a Choke Valve in the Carburetor?


What is a choke valve in the carburetor- 

For starting the cold engine, a rich mixture is needed. To provide a rich mixture, a choke valve is fitted in the air intake passage of the carburetor. The choke valve is in the form of a circular disc like the throttle valve. This choke valve is operated to shut off partially the supply of air to the carburetor(the valve “chokes off” the air supply). During the suction stroke, less amount of air and more amount of fuel is sucked, thus a rich mixture is obtained. The quantity delivered is sufficient to produce the correct air-fuel mixture needed for starting the cold engine.


As soon as the engine starts, its speed increases, and a lean mixture is needed. Thus, the choke valve must be operated to open the air supply otherwise the engine will be flooded with fuel. Due to the storage of air, unburned fuel will be exhausted, and the engine will not take a full load. Thus, immediately after starting the cold engine, the choke valve should be opened for full air supply.


Working of a choke valve in the carburetor- 

Working of a choke valve in the carburetor
Choke system in operation.


In most passenger carburetors, the choke valves are operated automatically by the thermostat. The valve is held in a partially closed position by the thermostat when the engine is being started and is opened automatically as the engine heats up, gradually leaning down the mixture. In some cars, hand-operated choke valves are used. In bikes, there are hand-operated choke valves are available. The choke valve is operated through the linkage by a knob on the instrument panel. 

The figure shows the choke system in operation. Details, of the choke system, are shown in the figure. The choke system consists of a choke shaft, choke lever assembly, screws, and a means of controlling the piston of the valve. The choke shaft is generally off-center so that one side of the valve has a larger area than the other. This unbalanced condition helps in opening the valve during the engine operation due to the greater force of the incoming air on the larger surface. 

Why BS-6 engines do not need any choke valve? 

The BS-6 emission norms were introduced in India in April 2020. They represent a significant step forward in reducing air pollution caused by vehicles. As part of the new regulations, many two-wheeler manufacturers have eliminated the choke button from their bikes.

In the past, the choke button was a common feature on two-wheelers, particularly those with carbureted engines. However, the process of the choke valve resulted in higher levels of emissions, particularly of carbon monoxide and hydrocarbons. Two-wheeler manufacturers have had to make significant changes to their engines in order to comply with the stricter emissions standards. One of the key changes has been the introduction of fuel injection technology, which is more precise and efficient than carburetors. Fuel injection systems are able to adjust the air-fuel ratio automatically based on factors such as engine temperature and load. The system is totally operated electronically. So there is no need for valves like a choke.

Another factor that has contributed to the elimination of the choke button is the increasing use of electric starters on two-wheelers. In the past, kick-starting a cold engine required a richer fuel mixture, which was achieved by using the choke button. However, electric starters are able to turn the engine over at a sufficient speed even when the engine is cold, meaning that a richer fuel mixture is no longer necessary. The elimination of the choke button on BS6 two-wheelers is a result of the introduction of fuel injection technology and the increasing use of electric starters.

Conclusion of What is a Choke Valve in the Carburetor

The choke valve in a carburetor is designed to restrict the flow of air into the engine during cold starts, in order to create a richer fuel mixture that is easier to ignite. This is necessary because cold engines require a richer mixture than warm engines in order to run smoothly. But in the BS-6 engines, there are no choke valves and carburetors available. 
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