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CARBURETOR-AFB
14-59
PART 7
AFB CARTER
Description
The AFB (aluminum four barrel) carburetor con-
tains many features, some of which are the locations
for the step-up rods and pistons. The step-up rods,
pistons and springs are accessible for service without
removing the air horn or the carburetor from the en-
gine. The venturi assemblies (primary and secondary)
are replaceable and contain many of the calibration
points for both the high and low speed system. One
fuel bowl feeds both the primary and secondary noz-
zles on the right side while the other fuel bowl takes
care of the primary and secondary nozzles on the left
side. This provides improved performance in corner-
ing, quick stops and acceleration.
All the major castings of the carburetor are alumi-
num, with the throttle body cast integral with the
main body. This allows an overall height reduction in
the carburetor. The section containing the accelerator
pump is termed the primary side of the carburetor.
The rear section is the secondary. The five conven-
tional systems used in previous four barrel carburet-
CABURETORS
ors are also used in this unit. The five conventional
systems are, two float systems, two low speed sys-
tems, (primary side only) two high speed systems, one
accelerator pump system and one automatic choke
control system.
The AFB-3853s and AFB-3854s carburetors used
on vehicles with 273 cubic inch engines are equipped
with a pair of velocity valves, which control the sec-
ondary valve operation.
The throttle valves of the secondary half of the car-
buretor are mechanically connected to the primary
valves and open with the primary after an approxi-
mate 60" lag; and continue to open until both pri-
mary and secondary throttle valves reach the wide
open position simultaneously. As engine speed in-
creases, the forces exerted by the velocity of intake
air down through the venturis of the carburetor in-
creases and tends to overcome the counterweight at-
tached to the velocity shaft, permitting the offset
velocity valves to position themselves according to
engine requirements.
SERVICE PROCEDURES
DISASSEMBLY
To disassemble the carburetor for cleaning or over-
haul, refer to (Fig. l), then proceed as follows:
Air
Horn Removal
(1) Place the carburetor assembly on repair stand
Tool
C-3400
or T-109-287s elevating legs. These tools
are used to protect the throttle valves from damage
and to provide a suitable base for working.
(2) Remove the hairpin clip that attaches the fast
idle connector rod to the choke lever. Disengage rod
from lever, then swing rod at an arc until it can be
disengaged from the fast idle cam.
(3)
Remove the clevis pin that holds the throttle
connector rod in the center hole of the accelerator
pump arm. Remove the hairpin clip that attaches the
lower end of rod in the primary throttle shaft lever.
Disengage rod from arm and lever, then remove from
carburetor.
(4) Remove the screws attaching the step-up piston
and rod cover plates.
Hold cover down with a finger
to prevent the piston and rods from flying out.
Lift
off the plates and slide the step-up pistons and rods
out of the air horn, as shown in (Fig. 2). Remove the
step-up piston springs.
(5) Remove the vacuum hose between the carburet-
or throttle body and the vacuum diaphragm.
(6)
Remove the clip from the choke operating link
and disengage the link from the diaphragm plunger
(stem) and the choke lever. Refer to (Fig. 1 ) .
STEP-UP-
/=3h
STEP-UP
h
P I S T O N
AND
M E T E R I N G
S C R E W \
3
STEP-UP
O N
S P R I N G
c 0 " E R - e
PLATES
.
N K586
Fig. 2-Removing
or
Installing Step-up Pistons
and Rods
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