Why engine RPM's first increase and then decrease when the pilot add heat to the carburetor?

When a pilot adds heat to the carburetor, it initially increases engine RPM because the heat helps to vaporize the fuel, improving the fuel-air mixture and enhancing combustion efficiency. However, as the heat continues to rise, it can lead to a richer mixture or vapor lock, causing a decrease in engine performance and RPM. Additionally, excessive heat may also negatively affect the engine's overall efficiency and lead to an increase in the likelihood of engine knocking, resulting in a drop in RPM.