In a closed-feed injection carburetor, the discharge occurs under what pressure condition?

• A. Negative pressure
• B. Positive pressure
• C. Atmospheric pressure
• D. Vacuum pressure

Answer: (B)

In a closed-feed injection carburetor, fuel must be pushed into the incoming air stream. The intake manifold is under suction during the intake stroke, so to force fuel into that lower-pressure region you need the fuel discharge pressure to be higher than the manifold (and typically higher than atmospheric). That means the fuel is delivered at a positive pressure relative to ambient, not at vacuum or atmospheric pressure. With positive discharge pressure, the fuel sprays and atomizes properly into the moving air, giving accurate metering and good combustion.