What could result from a fuel supply that is excessively rich?

A fuel supply that is excessively rich means that there is an abundance of fuel in the air-fuel mixture entering the engine compared to the required amount necessary for complete combustion. When the mixture is too rich, it can lead to incomplete combustion, which means not all the fuel burns effectively during the combustion process. This inefficiency results in reduced combustion efficiency because some of the fuel goes unburned or partially burned.

In addition to decreased efficiency, an excessively rich mixture can also create distinct problems such as increased exhaust emissions, particularly hydrocarbons and carbon monoxide, as unburned fuel exits the engine. While improved engine response or higher fuel economy might be appealing outcomes, they are counterintuitive in the context of a rich fuel supply. Instead, the conditions under excessive richness overwhelmingly lead to combustion inefficiencies, making the reduction in combustion efficiency the most pertinent result.