What is the fuel-air ratio for best economy?

• A. Rich 1:12
• B. Lean 1:20
• C. Stoichiometric 14.7:1
• D. Lean 1:16

Answer: (D)

Best economy comes from using less fuel per unit of air, so the engine should run a lean mixture that is still stable and capable of smooth operation. For a typical gasoline engine, the stoichiometric balance is about 14.7 parts air for every part of fuel. To maximize fuel efficiency, you lean the mixture slightly, which reduces fuel consumption while keeping combustion reliable. Around 16 parts air per part fuel (a fuel–air ratio of about 1:16) is a common range for best economy.

Rich mixtures burn more fuel without providing extra useful power, so they waste fuel. A mixture much leaner than the optimal point can become unstable or cause rough running, so it wouldn’t give the best economy either. That’s why the lean 1:16 option is the best choice for economy among the given possibilities.