What happens if a carburetor is adjusted too lean?

When a carburetor is adjusted too lean, it means that there is an insufficient amount of fuel relative to air being mixed before it enters the engine. This imbalance results in a more fuel-efficient air-fuel mixture, but at the cost of temperature management within the engine. As a consequence of the lean mixture, the combustion process occurs with higher temperatures because the fuel is not adequately present to absorb heat during combustion.

Increased operating temperature can lead to several issues, including the risk of engine damage such as overheating, pre-ignition, and even potential engine knock. Components like valves and pistons are particularly susceptible to heat damage when the fuel isn't sufficient to maintain safe operating temperatures.

The other options relate to fuel consumption, engine temperature reduction, and fuel stability—factors that do not align with the characteristics of a lean mixture, which prioritizes air over fuel and consequently increases the thermal load within the engine.