When carburetor heat is applied, does the fuel-air mixture become richer or leaner?

• A. The mixture becomes richer.
• B. The mixture becomes leaner.
• C. The mixture remains unchanged.
• D. The engine RPM increases.

Answer: (A)

Carburetor heat introduces warmer air into the carburetor, which makes the incoming air less dense. The fuel metering in a carburetor is tied to the amount of air flowing through the venturi. When the air is heated and its density drops, the same volume of air carries less mass, and the fuel flow doesn’t decrease in exact proportion. As a result, more fuel is present per unit of air, shifting the fuel–air ratio toward a richer mixture. In short, heating the air through carburetor heat tends to make the mixture richer.