As carburetor heat is applied, what occurs to the fuel-to-air ratio?

When carburetor heat is applied, it leads to a warmer intake air temperature entering the carburetor. Warmer air is less dense compared to cooler air. As a result, a volume of warmer air contains fewer air molecules than an equal volume of cooler air, which means that for a given amount of fuel, this reduces the overall density of the air entering the engine.

Because the engine requires a specific fuel-to-air ratio for optimal performance, applying carburetor heat effectively causes the air component of the mixture to decrease in density. The reduction in air density means that the existing amount of fuel is now in greater proportion to the diminished amount of air, thus making the mixture richer. A richer mixture consists of a higher proportion of fuel compared to the air, which can be necessary to prevent engine roughness or stalling, especially in conditions where ice may have formed in the carburetor.

This understanding ties back to the operations of a carburetor and how air temperature and density impact engine performance and fuel efficiency.