Air inlet Constant head idle spring Ball valve Air diaphragm Fuel diaphragm Impact tube Venturi suction Inlet air pressure Fuel inlet pressure Metered fuel pressure Line to flow divider Throttle valve Metering fuel pressure Unmetered fuel pressure Venturi Figure 2-31.  Airflow section of a fuel injector.  Under low power settings, the difference in pressure created  by the venturi is insufficient to accomplish consistent  regulation of the fuel. A constant-head idle spring is  incorporated to provide a constant fuel differential pressure.  This allows an adequate final flow in the idle range. models, a power enrichment jet is also located in this section.  The purpose of the fuel metering section is to meter and  control the fuel flow to the flow divider.  [Figure 2-35]  The  manual mixture control valve produces full rich condition  when the lever is against the rich stop, and a progressively  leaner mixture as the lever is moved toward idle cutoff. Both  idle speed and idle mixture may be adjusted externally to  meet individual engine requirements. The fuel metering section is attached to the air metering  section and contains an inlet fuel strainer, a manual mixture  control valve, an idle valve, and the main metering jet.  [Figure 2-34]  The idle valve is connected to the throttle valve  by means of an external adjustable link. In some injector  The metered fuel is delivered from the fuel control unit to a  pressurized flow divider. This unit keeps metered fuel under  Flow Divider Fuel Metering Section Figure 2-33.  Fuel diaphragm with ball valve attached. Figure 2-32.  Impact tubes for inlet air pressure. 2-23