Main Metering (High Speed) Circuit (2100-2 Venturi); Power Enrichment Circuit (2100-2 Venturi) - Jeep 1979 CJ-5 Technical & Service Manual

1J-22 FUEL SYSTEMS
From the main wells, the fuel is metered as it passes
through calibrated restrictions at the lower end of the
idle tubes. After flowing through the idle tubes, the fuel
enters diagonal passages above the tubes. The fuel is
metered again as it flows downward through restric-
tions at the lower end of the diagonal passages and then
enters the idle passages in the main body (fig. 1J-41).
Air enters the idle system through air bleeds which
are located in the main body directly below the booster
venturi. The air bleeds serve as anti-siphon vents during
off-idle, high speed operation and when the engine is
stopped.
The fuel-air mixture moves down the idle passages
past the idle transfer slots which serve as additional air
bleeds during curb idle operation. The fuel-air mixture
then moves past the idle mixture adjusting screw tips
which control the amount of discharge. From the adjust-
ing screw ports, the fuel-air mixture moves through
short horizontal passages and is discharged below the
throttle valves.
^ ANTI-SIPHON
A I R BLEED
IDLE
SCREW
PORT
Main Metering (High Speed) Circuit
As engine speed increases, the air velocity through the
booster venturi creates a low pressure area. Fuel flow
through the main metering circuit is caused by atmos-
pheric pressure in the fuel bowl and low pressure at the
main discharge ports. Fuel flows from the fuel bowl,
through the main jets and into the main wells. The fuel
then moves up the main well tubes where it is mixed
with air. The air, supplied through the main air bleeds,
mixes with the fuel through small holes in the sides of
the main well tubes. The main air bleeds meter an in-
creasing amount of air, whenever venturi vacuum in-
creases, to maintain the proper fuel-air ratio. The
mixture of fuel and air, being lighter than raw fuel,
responds quickly to changes in venturi vacuum. It also
atomizes more readily than raw fuel.
^ The fuel-air mixture moves from the main well tubes
to the discharge ports and is discharged into the booster
venturi (fig. 1J-42).
Anti-siphon air bleeds, located near the top of the
main well tubes, prevent siphoning of fuel from the
main well when decelerating.
ANTI-SIPHON
AIR BLEED
I D L E
L I M I T E R CAP 8 0 0 0 5
Fig. 1J-41
idle d r o i t
8 0 0 0 6
At speeds slightly above idle, the idle transfer slots
begin discharging the fuel-air mixture as the throttle
valves expose them to manifold vacuum. As the throttle
valves continue opening and engine speed increases, the
airflow through the carburetor increases proportion-
ately. This increased airflow creates a vacuum in the
venturi and the main metering system begins dis-
charging a fuel-air mixture. The discharge from the idle
circuit tapers off as the main metering circuit begins
discharging.
Fig. 1J-42 RSain Metering Circuit
Power Enrichment Circuit
During heavy load conditions or high speed operation,
the fuel-air ratio must be increased for higher engine
output. The power enrichment circuit supplies extra fuel
during this period and is controlled by intake manifold
vacuum (fig. 1J-43).