EMISSION CONTROLS AND FUEL SYSTEM 155
AFB main body components
Clearance between the positive closing
shoes on the primary and secondary throttle
valves is checked with the valves closed. Bend
the secondary closing as required to obtain a
clearance of 0.20 in.
The secondary throttle opening is gov-
erned by the pick-up lever on the primary
throttle shaft. It has two points of contact with
the loose lever on the primary shaft. If the
contact points do not simultaneously engage,
bend the pick-up lever to obtain proper en-
gagement. The primary and secondary throt-
tle valve opening must be synchronized.
DISASSEMBLY AND ASSEMBLY
1. Remove the pump rod and intermedi
ate choke rod. Remove the outer lever and
washer from the choke staft, then remove the
inner lever and fast-idle rod as an assembly.
Remove the step-up position cover plates,
piston, and step-up rod and spring. Lightly
tap the fuel inlet fitting. Before removing it,
remove its gasket and strainer then carefully
lift the top cover to protect the floats and
pump plunger from damage.
2. Remove the float lever pins, floats, float
needles, seats, and gaskets. Keep separate to
avoid unnecessary adjustment. Remove the
pump plunger lever, S link, plunger, and
cover gasket.
3. Do not remove the choke valve and
shaft(s) unless there is obvious shaft binding
or damage to the valve.
4. Remove the accelerator-pump lower
spring and, after checking the fuel for con
tamination, drain the bowl. Sweep a magnet
around the bottom of the bowl while fuel is
still present to capture iron oxide dust or
metal particles which may damage the needle
seats. Water contamination will appear as
milky globules at the bottom of the fuel bowl.
5. Remove the choke housing cover, gas
ket, and baffle. Remove the O-ring seal from
the vacuum opening in the mounting boss.
Remove the choke piston, levers, pump clus
ter and gasket, and pump discharge needle.
Remove the venturi cluster. The venturi as
semblies are dissimilar and cannot be assem
bled in the wrong location. Primary venturi
gaskets differ from secondary.
6. Remove the secondary auxiliary valves,
idle-mixture screws and springs, and all four
metering jets. Metering rods are used in the
primary metering jets and these jets are visi
bly larger than their secondary counterparts.
Remove the pump intake check valve and seat
assembly.
7. Wash all parts except the choke coil
housing and the pump plunger in carburetor
cleaning solution. Clean the choke housing in
gasoline.
8. Reassembly is the reversal of this pro
cedure.
Rochester 4MC, 4MV, M4MC,
and E4ME Carburetors
The Rochester Quadrajet® carburetor is a two
stage, four-barrel downdraft carburetor. The
designation MC or MV refers to the type of
choke system the carburetor is designed for.
The MV model is equipped with a manifold
mounted thermostatic choke coil. The MC
model has a choke housing and coil mounted
on the side of the float bowl.
The primary side of the carburetor is
equipped with 1% in. diameter bores and a
triple venturi with plain tube nozzles. Dur-
ing off idle and part throttle operation, the
fuel is metered through tapered metering rods
operating in specially designed jets posi-
tioned by a manifold vacuum responsive pis-
ton.
The secondary side of the carburetor con-
tains two 2?4 in. bores. An air valve is used
on the secondary side for metering control and
supplements the primary bores.
The secondary valve operates tapered me-
tering rods which regulate the fuel in con-
stant proportion to the air being supplied.
E4ME carburetors are used only on 1980— 81
engines equipped with computer con-
trolled emissions systems. NOTE:
E4ME
carburetors should be serviced only by
professional service technicians.
PUMP INTAKE
PRIMARY
CHECK BAU
VENTURI
CLUSTER
