In carb engines the inlet valves are cooled by

• A. incoming mixture
• B. air cooled
• C. oil spray
• D. water jacket

Answer: (A)

The intake valve is cooled mainly by the incoming air–fuel mixture. When the valve is open, the fresh charge flows across the valve face and stem, and its cooler temperature relative to the hot valve allows heat to be carried away by convection and, to some extent, by the vaporization of fuel. This direct contact with the charge provides the primary cooling for the inlet valve in a carbureted engine.

While the engine’s cooling system (water jacket) and lubrication (oil spray) contribute to overall temperature control, they do not provide the immediate, valve-face cooling that the passing mixture delivers. Air cooling of the valve isn’t the principal method here because the valve’s position inside the head limits direct exposure to ambient air, whereas the incoming mixture reliably streams over it during operation.