If the air-fuel ratio is enriched above 0.080, what happens?

• A. Increased power and higher temperature
• B. Loss of power and lower temperature
• C. No change in performance
• D. Loss of power but higher temperature

Answer: (B)

When the air-fuel ratio is enriched beyond the ideal mix, there is more fuel relative to air than needed for complete combustion. That extra fuel uses heat to vaporize and doesn’t all burn efficiently because there isn’t enough oxygen to support a complete burn. As a result, the combustion process is less efficient, the pressure rise inside the cylinder is smaller, and the engine loses power. The added fuel also absorbs heat, which lowers the peak combustion temperature.

So, enriching the mixture above this point leads to a drop in power and a lower combustion temperature. The other outcomes—more power or higher temperature—don’t align with the effects of a too-rich mixture, and a change in performance is expected rather than none.