Buick LeSabre 1965 Service Manual page 134

3 - 5 8 4-BARREL CARTER
ENGINE FUEL AND EXHAUST
SECTION 3-H
CARTER DUAL 4-BARREL CARBURETORS
CONTENTS OF SECTION 3-H
Paragraph Subject
Page Paragraph Subject
Page
3-26 Description and Operation of Carter
Dual 4-Barrel Carburetors 6-58
3-27 Servicing Carter Dual 4-Barrel
Carburetors 3-58
3-28 Throttle Linkage Adjustments - Dual
4-Barrel Carburetors 3-58
3-29 Idle Speed and Mixture Adjustments-
Dual 4-Barrel Carburetors 3-60
3 - 2 6 DESCRIPTION AND
OPERATION OF
CARTER DUAL
4-BARREL
CARBURETORS
The Carter Model AFB 4-barrel
carburetors used in the 425 cubic
inch engine dual 4-barrel option
are very s i m i l a r to single
4-barrel Carter carburetors. To
aid in description, the carbu-
retors will be referred to as
front and rear carburetors. Each
carburetor, of course, has a pri-
mary section (consisting of the
2-barrelled forward half) and a
secondary section (consisting of
the 2-barrelled rearward half).
Although fuel for idling is sup-
plied by the primary section of
both carburetors, fuel for all
other operation except for hard
acceleration or extreme high
speeds is provided by the primary
section of the rear carburetor
only. Only the rear carburetor
is equipped with an automatic
choke and a clean air system for
the choke. The rear carburetor
also provides connections for the
positive crankcase ventilator and
the distributor vacuum advance
unit.
The front carburetor (primary
section) has fixed idle orifices.
Only the rear carburetor (pri-
mary section) has idle mixture
adjusting needles and an idle
speed adjustment. This speed ad-
justment is of the idle by-pass
type; all throttle valves are
closed tight, so all air flow at
idle is metered by a single brass
air adjustment screw in a by-
pass channel.
Operation of the dual carburetor
system from idle to wide open
is as follows: As the accelerator
pedal is gradually depressed, the
primary of the rear carburetor
starts to open. When it is ap-
proximately half open, the pri-
mary of the front carburetor
starts to open. Next the secon-
dary of the rear carburetor starts
to open, and last, the secondary
of the front carburetor starts to
open. Each of the four sections
opens at such a rate that all
throttle valves reach the wide
open position at the same time.
3 - 2 7 SERVICING CARTER
DUAL 4-BARREL
CARBURETORS
The disassembly, cleaning, in-
spection and assembly procedures
are the same as in Section 3-G.
The internal and external carbu-
retor adjustments are also made
in a similar manner, but some of
the dimensions differ from those
for the single 4-barrel Carter.
For dual 4-barrel specifications,
see page 3-2.
3 - 2 8 THROTTLE LINKAGE
ADJUSTMENTS-
DUAL 4-BARREL
CARBURETORS
a. Throttle Linkage
Adjustments
1. Move rear carburetor throttle
lever to wide open position, mak-
ing sure that nothing prevents
lever from actually contacting
carburetor casting.
2. Unsnap front end of rear throt-
tle rod assembly from throttle
lever. While another man presses
accelerator pedal firmly against
floor mat, hold rear throttle in
wide open position and adjust rear
throttle rod length so that its
socket aligns with the ball on
the throttle lever. Then shorten
rear throttle rod two turns and
snap socket on throttle lever ball.
3. With both carburetors held at
closed throttle, adjust turnbuckle
until it just contacts trunnion of
front carburetor, then back-off
turnbuckle one turn and tighten
lock nut. See Figure 3-83.
4. With both carburetors held at
wide open throttle, adjust bolt
until it just contacts trunnion of
front carburetor. (Bolt is self-
locking. )