PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 1/TASK 2
opening, or by providing a second supply of fuel from the float bowl. Three
basic highspeed enrichment systems are power jet, vacuumoperated metering
rod, and mechanically operated metering rod.
(a) Power Jet (figure 17). The power jet system includes a jet
that is opened by a vacuum operated piston. The jet provides an extra
supply of fuel to the discharge nozzle from the float bowl. When the
throttle valve is not opened wide, there will be high manifold vacuum
because the carburetor throat is restricted. This high manifold vacuum is
used to hold the vacuum piston against its spring. When the piston is up,
the spring in the power jet will hold it closed. The throttle valve is
opened when extra power is demanded, causing a drop in manifold vacuum. As
manifold vacuum drops, the spring on the vacuum
FIGURE 17. VACUUM POWER JET.