When carburetor heat is applied, what happens to the fuel-to-air ratio?

• A. The engine will stall
• B. The fuel-to-air ratio becomes leaner because air density increases
• C. The fuel gets richer because the air becomes less dense (enriching)
• D. The mixture remains unchanged

Answer: (C)

When carburetor heat is used, the incoming air becomes warmer and less dense. The carburetor meters fuel in rough proportion to the amount of air flowing through it, so with less dense air flowing for the same volume, the fuel-to-air ratio shifts toward more fuel per unit of air. In other words, the mixture becomes richer because the air is less dense.