What can cause excessive tailpipe emissions?

An incorrect air-fuel mixture can lead to excessive tailpipe emissions because it disrupts the optimal combustion process in the engine. When the mixture is too rich (too much fuel in relation to air), it means there is insufficient oxygen to allow for complete combustion. This can result in the production of unburned hydrocarbons and carbon monoxide, which are harmful pollutants found in tailpipe emissions. Conversely, if the mixture is too lean (too much air in relation to fuel), it can lead to increased nitrogen oxides emissions due to higher combustion temperatures. Thus, maintaining a proper air-fuel mixture is crucial for minimizing emissions and ensuring a cleaner exhaust.