When black smoke is being emitted from a tailpipe, what does this indicate?

When black smoke is emitted from a tailpipe, it is an indication that the engine is running with a mixture that is too rich. A rich mixture means that there is an excessive amount of fuel in relation to the amount of air being used in the combustion process. This can lead to incomplete combustion, resulting in unburned fuel being expelled from the exhaust as black smoke.

In a properly balanced air-fuel mixture, the combustion process should produce minimal to no smoke. The appearance of black smoke suggests that the engine is not utilizing the fuel efficiently, which may be caused by various factors such as faulty fuel injectors, a malfunctioning carburetor, or issues with the engine control unit. Recognizing this symptom is crucial for diagnosing engine performance issues, as it can lead to higher emissions, reduced fuel economy, and potential damage over time if not addressed.