Carburetor Working Principle-Main Parts, Function, Advantages and Disadvantages of Carburetor

Carburetor Working:

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Main Parts of Carburetor:

Float Chamber:   

  • The float chamber serves as a storage tank of fuel for a continuous supply of fuel.
  • It contains a float valve which maintains the level of fuel in the float chamber. When the level of fuel decreases in float chamber the float moves downward, which open the fuel supply valve and allow the flow of fuel into the float chamber.
  • As the fuel level increases, the float moves upward which close and stop the fuel supply.


  • It is a device which is used to filter the fuel before entering into the float chamber.
  • It consists of a fine wire mesh which filters the fuel and removes dust and other suspended particles from it. If these particles not removed, can cause blockage of the nozzle.

Metering System:

  • The metering system controls the flow of fuel into the nozzle. It is responsible to form a correct mixture of air fuel.  
  • It consists of two main parts 1. Metering orifice and 2.  Fuel discharge nozzle.
  • When the air passes through venturi, it generates a low-pressure field across the throat. Due to this pressure difference, fuel is discharged into the air stream. The quantity of fuel is control by the metering orifice and discharge hole at the exit of the fuel discharge nozzle.
Carburetor Working
Carburetor Working

Idling System:

  • The idling system consists of a passage directly from the float chamber to the venturi tube. It provides a rich mixture during idling and at low speed. It works during idling or when the throttle is open below 15%.

Throttle Valve:

  • It is a butterfly valve situated at the exit of the venturi tube. It controls the speed of the vehicle by providing control amount of mixture. It controls the quantity of air-fuel mixture.
  • If the throttle is fully opened, then more mixture is drawn into the cylinder and thus gives high output.

Choke Valve:

  • It is the same as the throttle valve in construction but situated at the entrance of the venturi tube.
  • It is used to provide very rich mixture during starting in cold season. It controls the quantity of air flow through the venturi tube. If the choke is fully open, normal amount of air flow through venturi, which forms a normal mixture.
  • But if the choke is partially closed, it results, low amount of air flow through venturi and a large amount of fuel flow through the discharge nozzle. It gives a rich mixture.

Carburetor Working:

  • The Simple carburetor mainly consists of a float chamber, Fuel discharge nozzle, a metering orifice, a venturi, a throttle valve and a choke.
  • The Float and needle valve system maintains a constant level of gasoline in the float chamber.
  • If the amount of the fuel in the float chamber falls below the designed level, the float goes down, thereby opening the fuel supply valve and admitting fuel. when the designed level has been reached, the float closes the fuel supply valve thus stoping additional fuel flow from the supply system.
Carburetor Working
Carburetor Working
  • Float chamber is vented either to the atmosphere or to the upstream side of the venturi.
  • During the suction stroke, air is drawn through the venturi. Venturi is a tube of decreasing cross-section with a minimum area at the throat.
  • Venturi tube is also known as a choke tube and is so shaped that it offers minimum resistance to the air flow. As the air passes through the venturi the velocity increase reaching a maximum at the venturi throat. Correspondingly, the pressure decreases reaching a minimum.
  • From the float chamber, the fuel is fed to a discharge jet, the tip of which is located in the throat of the venturi.
  • Because of the differential pressure between the float chamber and the throat of the venturi, known as carburetor depression, fuel is discharged into the air stream.
  • The fuel discharged is affected by the size of the discharge jet and it is chosen to give the required Air fuel ratio.

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Function of carburetor:

  • The main function of carburetors to mix air and gasoline and provides a high combustion mixture.
  • It controls the engine speed.
  • It also regulates the air-fuel ratio.
  • Increase or decrease the amount of mixture according to the engine speed and load changing.

Advantages :

  • Carburetor parts are not as expensive as that of fuel injectors.
  • With the use of a carburetor, you get more air and fuel mixture.
  • In terms of a road test, carburetors have more power and precision.
  • Carburetors are not restricted by the amount of gas pumped from the fuel tank which means that cylinders may pull more fuel through the carburetor that would lead to the denser mixture in the chamber and greater power as well.

Disadvantages :

  • At a very low speed, the mixture supplied by a carburetor is so weak that, it will not ignite properly and for its enrichment, at such conditions, some arrangement in the carburetor is required.
  • The working of a carburetor is affected by changes in atmospheric pressure. 
  • More fuels are consumed since carburetors are heavier than fuel injectors.
  • More air emissions than fuel injectors.
  • Maintenance costs of a carburetor are higher than the fuel injection system.

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