The function of the carburetor is to supply the proper fuel-air ratio to the engine cylinder during suction created by the downward movement of the piston. As the piston moves downward a pressure difference is created between the atmosphere and the cylinder which leads to the suction of air in the cylinder. This sucked air will also carry with it some droplets of fuel discharged from a tube. The tube has an orifice called carburetor jet which is open to the path of sucked air. The rate at which fuel is discharged into the air will depend upon the pressure difference created. To ensure the atomization of fuel the suction effect must be strong and the fuel outlet should be small.

Working of Simple Carburetor: To increase the suction effect the passage of air is made narrow. It is made in the form of venturi. The opening of the fuel jet is placed at the venturi where the suction is greatest because the velocity of air will be maximum at that point.

The fig. shows a simple carburetor consists of float chamber, nozzle, a venturi, a choke valve and a throttle valve. The narrow passage is called venturi. The opening of the fuel is normally placed a little below the venturi section. The atomized fuel and air is mixed at this place and then supplied to the intake manifold of the cylinder. The fuel is supplied to the fuel jet from the float chamber and the supply of the fuel to the float chamber is regulated by the float pivot and supply valve. As the fuel level in the chamber decreases the float pivot will open the supply of the fuel from fuel tank.

As the air velocity of air passes through the venturi section will be maximum correspondingly the pressure will be minimum. Due to the pressure difference between the float chamber and the throat of the venturi, fuel is discharged from the jet to the air. To prevent the overflow of fuel from the jet, the level of fuel in the chamber is kept at a level slightly below the tip.

The quantity of the fuel supplied is governed by the opening of the butterfly valve situated after the venturi tube. As the opening of the valve is small, a less quantity of fuel-air mixture is supplied to the cylinder which results in reduced power output. If the opening of the valve is more then an increased quantity of fuel is supplied to the cylinder which results in greater output.

Types of Carburetors:

1. Solex Carburetor

2. Carter carburetor

3. S.U. Carburetor

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