Carburetors
In the operation of the float-type carburetor system, the outside air first flows through an air filter, usually located at an air intake in the front part of the engine cowling. This filtered air flows into the carburetor and through a venturi, a narrow throat in the carburetor. When the air flows through the venturi, a low-pressure area is created that forces the fuel to flow through a main fuel jet located at the throat.
Carburetor Icing
Carburetor ice occurs due to the effect of fuel vaporization and the decrease in air pressure in the venturi, which causes a sharp temperature drop in the carburetor.
If water vapor in the air condenses when the carburetor temperature is at or below freezing, ice may form on internal surfaces of the carburetor, including the throttle valve.
Carburetor ice is most likely to occur when temperatures are below 70°F (°F) and the relative humidity is above 80%.
Due to the sudden cooling that takes place in the carburetor, icing can occur even in outside air temperatures as high as 100°F and humidity as low as 50%.