Chevrolet 10 Series 1967, Service Manual

Page: 326 / 605

ENGINE FUEL 6M-2
M IX T U R E
Fig . 3C - Rochester 2 G Fig. 4C - Rochester 4 G
SERVICE PROCEDURES
Preliminary Checks
1. Thoroughly warm-up engine. If the engine is cold,
allow to run for at least 15 minutes.
2. Inspect torque of carburetor to intake manifold bolts
and intake manifold to cylinder head bolts to exclude
the possibility of air leaks.
3. Inspect manifold heat control valve (if used) for free­
dom of action and correct spring tension.
Idle Speed and Mixture Adjustment (Except Air Injection
Reactor System)
NOTE: This adjustment should be performed
with engine at operating temperature and parking
brake applied.
1
.
2
.
3.
Remove Air Cleaner.
Connect tachometer and vacuum gauge to engine, then
set hand brake and shift transmission into neutral.
As a preliminary adjustment, turn idle mixture
screws lightly to seat and back out
1
-
1 / 2
turns.
CAUTION:
Do not turn idle mixture screw
tightly against seat or damage may result.
4. With engine running (choke wide open) adjust idle
speed screw to specified idle speed, (automatic
transmission in drive, synchronized transmission in
neutral).
5. Adjust idle mixture screw to obtain highest steady
vacuum at specified idle speed.
NOTE:
On air conditioned vehicles, turn air
conditioning to the "on" position and hold the hot
idle compensator valve closed while adjusting
idle speed and idle mixture screws.
NOTE:
On Rochester B carburetors the idle
mixture screw should be turned out 1/4 turn
from the "lean roll" position. The definition of
"lean roll" point is a 20 to 30 rpm drop in en­
gine speed obtained by leaning the idle mixture.
6
. Repeat Steps 4 and 5 as needed for final adjustment.
NOTE: If necessary, final adjustment of the
carburetor may be made with the air cleaner
installed.
7. Shut down the engine, remove gauges and install air
cleaner.
Idle Speed and Mixture Adjustment (With Air Injection
Reactor System)
The following is the recommended procedure for Air
Injection Reactor System equipped engines.
NOTE:
This adjustment should be performed
with engine at operating temperature and parking
brake applied.
1
.
2
.
3.
4.
5.
Remove air cleaner.
Connect tachometer to engine, then set hand brake
and shift transmission into neutral.
As a preliminary adjustment, turn idle mixture
screws lightly to seat and back out 3 turns.
CAUTION: Do not turn idle mixture screw
tightly against seat or damage may result.
With engine running (choke wide open) adjust idle
speed screw to specified idle speed, (automatic
transmission in drive, synchronized transmission in
neutral).
Adjust idle mixture screw (turn in) to "lean roll"
position; then turn screw out 1/4 turn (1/4 turn rich
from "lean roll"). The definition of "lean roll"
point is a 20 to 30 rpm drop in engine speed, obtained
by leaning the idle mixture.
NOTE: On air conditioned vehicles, turn air
conditioning "O FF" on in-line, 283, and 327 cu.
in. engines.
6
. Repeat steps 3 and 4 as needed for final adjustment.
NOTE: If necessary, final adjustment of the
carburetor may be made with air cleaner
installed.
7. Turn off engine, remove gauges and install air
cleaner.
Choke Adjustment
1. Remove air cleaner.
2. Push hand choke knob in to within 1/8" of instrument
panel.
CHEVROLET TRUCK SERVICE M ANUAL