An air/fuel ratio of 9:1 would be considered:

An air/fuel ratio of 9:1 indicates that there are 9 parts of air for every 1 part of fuel. In combustion engine operation, the term "rich" refers to a mixture where there is more fuel relative to air than what is considered chemically correct for complete combustion. A chemically correct or stoichiometric air/fuel ratio for gasoline engines is typically around 14.7:1. Since 9:1 has significantly more fuel than the stoichiometric requirement, it is categorized as a rich mixture.

A rich air/fuel ratio can enhance power output and performance up to a certain point, particularly during conditions requiring more energy, such as acceleration or heavy load. However, it can also lead to incomplete combustion, increased emissions, and potential fouling of engine components. Thus, understanding that a 9:1 ratio provides excess fuel helps in recognizing its designation as rich.