PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 1/TASK 2
CONTROLLING FUEL BOWL PRESSURE.
(b) Idle Vent. Because gasoline is highly volatile, it can create
overly rich mixtures during long periods of engine idle. This is because
the fuel begins to evaporate in the float bowl and the vapors get into the
air horn through the balance tube. The solution to this problem is to have
an outside vent for the float bowl which is opened whenever the engine is
idling. The idle vent is activated by linkage from the throttle valve. The
idle vent system on later vehicles may be part of the emission control
Systems of the Carburetor
a. General. The two operating systems of the carburetor each contain
two circuits providing the flexibility to operate throughout the entire
engine speed range.
Both of these systems obtain gasoline from the float
bowl through the main jet (figure 14 on the following page). The main jet
is a precisely sized opening that helps govern the amount of fuel used. The
main jet is usually replaceable and is available in a variety of sizes.
Carburetors can be tailored to meet various needs by varying jet sizes. In
addition to the above, the carburetor must provide other systems to
compensate for temperature change and for quick changes in throttle