What issue may cause a lean mixture and high cylinder temperature?

A defective automatic mixture control unit can lead to a lean mixture because it is responsible for adjusting the fuel-air mixture in response to various operating conditions. When this control unit malfunctions, it fails to supply the necessary amount of fuel for the air entering the cylinders. This results in a lean mixture, where there is more air than fuel. A lean mixture can cause the engine to run hotter because there is insufficient fuel to effectively cool the combustion process. Consequently, the increase in cylinder temperature can lead to engine performance issues and potential damage if not addressed.

Understanding how the automatic mixture control unit operates is crucial, as it plays a vital role in maintaining the correct air-fuel ratio, ensuring the engine runs efficiently and safely. Clogged fuel lines and excessive fuel pressure typically contribute to rich mixtures, while an overly rich fuel mixture directly contradicts the conditions described in the question. Therefore, the functionality of the automatic mixture control unit is central to maintaining the desired mixture and, ultimately, engine health.