The carburetor is an integral part of the internal combustion engine. Internal combustion engines operate by igniting a mix of fuel and air. The fuel, typically gasoline, and air are trapped in combustion chambers in the engine block. An engine's engine block is made up of several combustion chambers, also known as cylinders, that are cast together in a parallel configuration. The cylinders have moveable pistons at one end. When the cylinders are filled with the carefully regulated mix of fuel and air, the mix is ignited by the spark plugs. The resulting explosion pushes the piston out of the cylinder, which powers the engine.
Ensuring that the air and fuel are mixed properly and are in the correct proportions is the function of the carburetor. A carburetor that is not working properly can add too much fuel, which "floods" the engine and keeps it from running properly. It can also add too much air to the mix, which will not ignite, also keeping the engine from running properly.
In a conventional carburetor, the action of the piston rebounding from the explosion returns the piston into the cylinder, drawing air through the carburetor. This causes the pressure in the carburetor to drop, drawing fuel into the carburetor to rest in a bowl containing a float. When the float reaches the top of the bowl, it closes the valve so that no more fuel can get in. As the fuel is used up, the float lowers, re-opening the valve to allow more fuel in. In a constant velocity carburetor, also known as a CV carburetor, the process is different.
A constant velocity carburetor has a device called a venturi, which is a tube through which the air enters the carburetor. The venturi is shaped like a funnel, narrowing at one end in order to change the air pressure of the air entering the carburetor. The narrow end lowers the pressure of the air, creating a comparative vacuum, which pulls fuel into the carburetor. The vacuum effect of the venturi is constant, providing a constant and consistent stream of fuel into the carburetor, as opposed to the pumping effect of a conventional carburetor.
