Which engine issue is likely to occur during low RPM and rich mixture settings?

Fouled spark plugs are a common issue that can occur during low RPM and rich mixture settings. When an engine runs with a rich mixture, there is an excess of fuel relative to the amount of air. This rich condition can lead to incomplete combustion, which causes carbon deposits to build up on the spark plugs. At low RPMs, the engine may not generate enough heat to burn off these deposits, further exacerbating the fouling. As a result, the spark plugs can become coated with carbon, leading to reduced efficiency, misfires, and potential starting difficulties.

In contrast, vapor lock typically occurs in hot conditions where fuel vaporizes in the fuel lines, not directly related to rich mixtures at low RPMs. Fuel starvation is more associated with issues like fuel pump failure or clogged filters rather than the specific conditions of low RPM and excessively rich mixtures. Lastly, excessive engine heat is more often linked to lean mixtures, where insufficient fuel leads to high combustion temperatures rather than rich mixtures, which can actually cool cylinder temperatures to some extent due to the increased fuel presence.