drop in proportion with the partial vacuum in the boost venturi. At the same time, air entering the carburetor compresses the air in the impact tubes, generating a positive pressure in chamber B that is proportional to the density and speed of the air entering the engine. The difference in pressure between chamber A and chamber B creates the air metering force which opens the servo valve allowing the fuel into the fuel regulator. The pressure of fuel from the fuel pump pushes against the diaphragm in chamber C, moving the servo valve toward the closed position. The fuel also flows to the mixture control valve, which is closed when in the idle-cutoff position and open in all other positions. Chamber C and chamber D are connected by a fuel passage which contains the fuel metering jets. When the mixture control lever is moved from the idle-cutoff position, fuel starts to flow through the metering jets and into chamber D where it becomes metered fuel. The discharge valve is spring-loaded to a preset pressure discharge pressure, acting as a variable size restriction to hold a constant pressure in chamber D, despite varying fuel flow rates. The valve is opened as the discharge fuel pressure increases above the force from the spring, thereby lowering the fuel pressure to maintain a balanced position with the spring force. The fuel mixture is automatically altitude-controlled by the automatic mixture control. It operates by bleeding higher pressure air from chamber B into chamber A as it flows through a tapered needle valve. The needle valve is controlled by an aneroid bellows that senses barometric pressure, causing a leaning of the mixture as altitude increases. Once airborne and having reached the cruising altitude, the pilot moves the mixture control from auto rich to auto lean. This reduces fuel flow by closing the passageway through the rich jet. The resulting reduction of flow unbalances the fuel metering diaphragm, causing the fuel metering valve to change position, thereby reducing fuel flow to the auto lean flow setting. In the event of a combat or emergency situation, the mixture control may be moved to the auto rich position, providing extra fuel to the engine, or in military aircraft, into military position, if the aircraft is so equipped. When in the military position, the Anti-Detonation Injection (ADI) system is activated, injecting the ADI fluid into the engine intake system. The