Dena Smith, age 16, of Bessemer, Ala., for his question:
HOW DOES A CARBURETOR WORK?
A carburetor is part of a gasoline engine. It provides the mixture of gasoline and air that the engine burns.
The simplest carburetor is a metal tube. Air enters at one end. Gasoline is mixed with air in the middle and gasoline air vapor is pushed from the other end of the carburetor into the engine.
A carburetor must mix the gasoline with about 15 times its weight in air for the engine to run smoothly at all speeds. A driver controls the engine speed by increasing or reducing the flow of the fuel mixture.
The float chamber of the carburetor stores a small amount of gasoline that is pumped to it from the main gasoline tank. When the chamber is full, a float resting on the top of the gasoline closes a valve in the fuel line. When gasoline is used by the engine, the float drops. This opens the valve in the fuel line and lets more gasoline flow into the chamber. The float keeps a steady level of gasoline in the chamber.
The air cleaner is placed at the top of the carburetor to remove dust from the air that is to be mixed with the gasoline since dust would cause wear to the engine. Atmospheric pressure pushes the air through a filter inside the cleaner.
The inside of the carburetor narrows to a small size, then widens out again. Its shape is called a Venturi. The Venturi increases the speed of the air rushing through the carburetor and lowers its pressure. The higher air pressure in the float chanmber then forces gasoline through the nozzle into the Venturi. The air picks up the gasoline and turns it into a vapor.
The intake manifold is fastened to the opposite end of the carburetor tube from the air cleaner. The intake manifold consists of a series of pipes that connect the carburetor with the engine cylinders. The gasoline air mixture flows through these pipes to the cylinders.
The throttle valve controls the engine speed by letting more or less of the gasoline air mixture enter the intake manifold. The driver presses the accelerator pedal to open the throttle valve. He lets up on the accelerator to close the throttle valve.
The choke valve looks like the throttle valve, but it controls the amount of air entering the carburetor. When it partly closes the carburetor tube, more gasoline and less air flow into the engine.
Choking the carburetor makes it easier for the spark plugs to ignite the gasoline air mixture when the engine is cold. The choke valve on many automobiles is controlled automatically by the temperature of the engine.
Carburetors are called updraft on downdraft according to their position. If the carburetor is below the intake manifold, it is updraft. If it is above, it is downdraft.