What is a common symptom of a vehicle running too rich?

A vehicle running too rich is characterized by an excessive amount of fuel being mixed with air in the combustion chamber. One of the most observable symptoms of this condition is excessive exhaust smoke, typically appearing as black smoke. This black smoke is primarily due to unburned fuel being expelled from the engine. When the air-fuel mixture is not balanced correctly, combustion becomes inefficient, leading to power loss and increased emissions.

In a rich running condition, the engine is unable to burn all the supplied fuel, hence causing that unburned fuel to escape through the exhaust system, resulting in the visible smoke. This is a clear indicator that the fuel mixture needs adjustment to achieve a proper balance for optimal engine performance. Other symptoms, such as poor acceleration and high fuel consumption, may also occur, but excessive exhaust smoke is a direct and common visual symptom of a rich mixture.