Additional Checks And Adjustments; Adjust Idle Speed; Cylinder Balance Test - Chevrolet CHEVY VAN G10 SERIES Service Manual

ADJUST IDLE SPEED (FIG. 17)
1. With engine running at operating tem perature, choke
valve in fully open position, parking brake on and drive
wheels blocked— adjust idle speed as follows (See " Tune-
U p" Decal Figure 18):
N O T E : A ll carburetors are equipped w ith
m ixture lim iter caps (Fig. 17); the idle m ixture is
preset and "locked in " by these caps—no attem p t
should be made to adjust m ixture. Do not remove
m ixture screw caps.
250 Cubic Inch (Single-Barrel Carburetor)
D isconnect " Fuel T ank " line from E vaporation Emission
vapor canister.
D isconnect the d istribu tor spark advance hose and plug the
vacuum source opening.
A djust Idle S top Solenoid screw to o b tain 700 rpm w ith
m anual transm ission in n eu tral; 600 rp m w ith autom atic
transm ission in drive. Do n o t adjust CEC Solenoid Screw.
C A U T IO N : If the CEC Solenoid Screw (Fig. 17) is
used to set engine idle or if the solenoid is adjusted
o u t o f limits as specified in Section 6 M , a decrease
in engine braking may result.
R econnect " Fuel T an k "
reconnect d istribu tor spark advance hose.
307 Cubic Inch (Two-Barrel Carburetor)
D isconnect the d istributor spark advance hose and plug the
vacuum source opening.
D isconnect " Fuel T ank" line from Evaporation Emission
vapor canister.
W ith air conditioning off, adjust Idle Stop Solenoid screw
to obtain 900 rpm w ith m anual transm ission in n eutral; 600
rpm w ith autom atic transm ission in drive.
With transm ission in park or neutral, adjust carb u reto r fast
idle cam screw to o btain 1850 rpm .
R econnect " Fuel T ank "
reconnect distribu to r spark advance hose.

ADDITIONAL CHECKS AND ADJUSTMENTS

C Y LIN D E R BALANCE TEST (FIG. 19)
It is o ften difficult to locate a w eak cylinder. A com ­
pression test, for exam ple, will n o t locate a leaky intake
m anifold, a valve n o t opening properly due to a w orn cam ­
shaft, or a defective spark plug.
With the cylinder balance test, the pow er o u tp u t o f one
cylinder may be checked against an other, using a set of
grounding leads. When the pow er o u tp u t o f each cylinder is
n o t equal, the engine will lose pow er and run roughly.
Perform a cylinder balance test as follows;
1. C onnect the tacho m eter and vacuum gauge.
2. S tart engine and ru n at 1500 rpm .
idle
line to vapor canister and
line to vapor canister and
VEHICLE EMISSION CONTROL INFORMATION
GEN ERAL M OTORS CORPORATION
MAKE ADJUSTMENTS WITH ENGINE AT NOtMAl OPERATING TEMPERATURE, (HOKE OPEN,
AND A ll CONDITIONING OFF. PLUG DISCONNECTED VACUUM FITTINGS.
SET P A R K IN G B RAKE A N D BLOC K DRIVE WHEELS.
1 DISCONNECT FUEL TANK HOSE FROM VAPOR CANISTER.
2. DISCONNECT DISTRIBUTOR VACUUM HOSE PlUG HOSE HADING TO CARBURETOR.
3. SET DWELL AND TIMING AT SPECIFIED RPM.
4. ADJUST IT TURNING CARBURETOR S0L£N0ID TO SPECIFIED RPM.
5. RECONNECT DISTRIBUTOR VACUUM HOSE AND FUEL TANK HOSE.
S(E SIMKE MANUAL FO B ADDITIONAL IMF0IMATI0M
w n ■ MAX THIS WHKlt CONFORM 10 FIOtlAl AI0 CALIFORNIA H W U II0B APWCAIU 10 1*72 MOW I TfAl MW M O TO R KKKIEV
VEHICLE EMISSION CONTROL INFORMATION . GENERAL MOTORS CORPORATION
TUNE-UP INSTRUCTIONS: (WITH ENGINE AT OPERATING TEMP, CHOKE OPEN. AIR CLEANER INSTALLED, AIR COND Off,
PARKING BRAKE ON)
1 DISCONNECT AND PLUG DISTRIBUTO R VACUUM HO SE, II
2 ADJUST C ARBURETO R S PEED SCREW TO SPE C IFIED R.P.M .
3 RECONNECT DISTRIBU TO R VACUUM HOSE
S E E S ER VIC E MANUAL FO R ADDITIONAL TUNE UP INFORMATION
FAM ILY 1 DISPLACEM ENT | TY P E | CARB
IS (NGM f C O N K X IM S 'O >10(1*1 tlOWAll
p H n o r\ f n K A t A Via
Fig. 1 8 —T u n e -U p Decal
350 Cubic Inch (Four-Barrel Carburetor)
On vehicles so equipped, disconnect " F uel T an k " line from
Evaporation Emission vapor canister.
D isconnect the d istrib uto r spark advance hose an d plug the
vacuum source opening.
On vehicles equipped w ith TCS system , turn air co nd itio n ­
ing o ff, adjust Idle S top Solenoid screw to obtain 800 rpm
w ith m anual transm ission in neutral; 600 rpm w ith autom atic
transm ission in drive.
On vehicles w ith o u t TCS system , adjust carburetor speed
screw to obtain 600 rpm w ith transm ission in neutral.
Place fast idle cam follow er on second step o f fast idle cam,
turn air conditioning " o f f ' and adjust fast idle to 1350 rpm
w ith m anual transm ission in neutral; 1500 rpm w ith autom atic
transm ission in "P ark" .
R econnect " Fuel T an k "
6
rec n n ect d istribu tor spark advance hose.
3. G round large clip o f grounding leads and connect
individual leads to all spark plugs except the pair being
tested.
Divide the firing order in half and arrange one h a lf over the
o ther. The cylinders to be tested to g eth er appear one over the
other.
6
L Firing Order
1-5.3-6-24 = 1-5-3 = 1-6, 5-2, 3-4
6-2-4
8
V Firing Order
1-8-4-3-6-5-7-2 = 1-8-4-3 = 1-6, 8-5, 4-7, 3-2
6-5-7-2
ENG INE 6-9
TRANSMISSION
AIR EXHAUST
MANUAL
EMISSION CONTROL AUTOMATIC
[ f t ]
DWELL 33° 33°
4° @ 600 4° @ 700
TIMING (°BTDC <3 RPM)
SPARK PlUG GAP .035 .035
R-46T R-44T
SPARK PLUG TYPE
SOLENOID ADJ (RPM) 600 (IN DRIVE) 700
IDLE MIXTURE PRESET AT FACTORY. DO NO! REMOVE CAPS
TMWt HUM— |
till
FUEL REQUIREMENTS—USE 91 OCTANE OR HIGHER.
fT. *0 . *271002
a
F U E L REQ UIREM ENTS— USE 91 OCTANE OR H IG HER.
line to vapor canister and
C H E V Y V A N SH O P M A N U A L