Carburetor Replacement (2100-2 Venturi); Carburetor Overhaul (2100-2 Venturi) - Jeep 1979 CJ-5 Technical & Service Manual

FUEL SYSTEMS
At the same time, the modulator arm contacts a tang-
on the choke shaft. The downward movement of the
diaphragm assembly compresses the piston spring and
exerts a pulling force on the modulator arm, causing the
choke valve to open slightly. This opening is known as
initial choke valve clearance.
PASSAGE AJ41647
Fig. 1J-45 Choke Circuit
As the engine begins to warm up, heated air from the
exhaust crossover is routed through a heat tube to the
choke housing. A thermostatic bypass valve, which is
integral with the choke heat tube, helps prevent pre-
mature choke valve opening during the early part of the
warmup period. The valve regulates the temperature of
the hot airflow to the choke housing by allowing outside
unheated air to enter the heat tube. A thermostatic disc
is incorporated in the valve which is calibrated to close
the valve at 75°F and open it at 55°F.
The heated air entering the choke housing causes the
thermostatic coil to begin unwinding and decreases the
closing force exerted against the choke valve. The coil
gradually loses its tension and allows the choke valve to
open.
When the engine reaches operating temperature, the
thermostatic coil continues unwinding and exerts pres-
sure against the choke linkage, forcing the choke valve
fully open. A continual flow of warm air passes through
the choke housing and is exhausted into the intake mani-
fold. The thermostatic coil remains heated and the choke
valve remains fully open until the engine is stopped and
allowed to cool.
Air flowing through the choke housing must be fil-
tered to minimize contamination of the choke coil and
associated parts. The air is supplied by a tube origina-
ting inside the air cleaner.
A fast idle is required to prevent engine stalling dur-
ing the warmup period. The fast idle cam, actuated by
the choke rod, contacts the fast idle speed adjustment
screw and increases engine speed in proportion to the
choke valve opening. When the choke valve reaches the
fully open position, the fast idle cam rotates free of the
fast idle speed adjusting screw, allowing the throttle
lever to return to curb idle.
If the engine is accelerated during the warmup period,
the resulting drop in manifold vacuum allows the ther-
mostatic coil to momentarily close the choke valve. This
provides a richer mixture to prevent engine stalling.
If the engine becomes flooded during the starting pe-
riod, the choke valve may be opened manually to purge
excess fuel from the intake manifold. This is accom-
plished by depressing the accelerator pedal to the floor
and cranking the engine. With the the accelerator link-
age in this position, a tang on the fast idle lever contacts
the fast idle cam, causing the choke valve to open a
predetermined amount. This is referred to as choke un-
loader clearance.
CARBURETOR REPLACEMENT
Removal
(1) Remove air cleaner.
(2) Remove accelerator cable from accelerator le-
ver. Disconnect vacuum hoses, pullback spring, choke
clean air tube, solenoid wire if equipped, PCV hose, in-
line fuel filter and choke heat tube at carburetor.
(3) Remove carburetor retaining nuts. Remove car-
buretor and gasket from intake manifold.
Installation
(1) Clean gasket mounting surfaces of spacer and
carburetor. Position gasket on intake manifold. Position
carburetor on spacer and gasket and install nuts. To
prevent leakage, distortion or damage to carburetor
body flange, alternately tighten nuts in crisscross
pattern.
(2) Connect in-line fuel filter, throttle cable, choke
heat tube, PCV hose, pullback spring, solenoid wire if
equipped, choke clean air tube and vacuum hoses.
(3) Adjust engine idle speed and idle fuel mixture.
Refer to Chapter 1A—General Service and Diagnosis for
procedures.
CARBURETOR OWERHAUL
The following procedure applies to complete overhaul
with the carburetor removed from the engine.
A complete disassembly is not necessary when per-
forming adjustments. In most cases, service adjust-
ments of individual systems may be completed without
removing the carburetor from the engine. Refer to Serv-
ice Adjustment Procedures.
A complete carburetor overhaul includes disassembly,
thorough cleaning, inspection, and replacement of all
gaskets and worn or damaged parts. Refer to figure 1J-
46 for parts identification.