1987 SUZUKI GRAND VITARA Service Repair Manual

[Switch vent solenoid]
Provided on top of the float chamber is a switch
vent solenoid which is connected to the ignition
switch through ECM. As the ignition switch is
operated, the solenoid opens and closes its valve
so as not to release the fuel vapor in the float
chamber out into the atmosphere.
When the ignition switch is turned to “OFF”
position, the passage connecting the inner vent
passage and the float chamber will close, and the
passage connecting the float chamber and the
canister will open, then the fuel vapor will flow
into the canister.
When the ignition switch is turned to “ON”
position, and engine speed is above 400 r/min,
the passage connecting the float chamber and
the canister will close, and the passage connect-
ing the float chamber and the inner vent passage
will open, then the fuel vapor will flow into the
carburetor bore.
1. Switch vent solenoid
2. Float
3. To canister
4. Inner vent passage
Fig. 4- l-4 Switch vent solenoid
Primary System
[Primary slow system]
The fuel, after passing through the main jet, is
metered by the primary slow jet, then mixed
with the air from the primary slow air No. 2
bleeder. This air/fuel mixture is further blended
with the air from the primary slow air No. 1
bleeder and air supplied through the mixture
control solenoid. Then the air/fuel mixture
passes through the idle down channel and enters
the carburetor bore through the off idle discharge
port and the idle discharge hole.
[Mixture control solenoid valve]
The primary system has the Mixture Control
Solenoid (MCS) Valve. In the MCS, there is a
plunger which makes 16 up and down move-
ments per second by the electrical signals from
the Electronic Control Module (ECM). That is,
when an electrical signal is received by the
solenoid, the plunger will move down and when
no signal is received, the plunger will move up
by the spring force.
When the plunger moves down, the air jet locat-
ed on the upper side of the mixture control
solenoid valve will open as shown in below
figure, allowing the air to flow into the idle
down channel. In this condition, the mixture
will become lean.
On the other hand, when the plunger is pushed
up by the spring, the air jet will close, shutting
off the air flow into the idle down channel. In
this condition, the mixture will become rich.
The up and down movement of the plunger at
the rate of 16 times per second to the signals
from the ECM controls the air/fuel mixture to
the optimum ratio at all times and as a result
helps to improve the emission and engine per-
formances, and fuel economy.
The ECM receives the electrical information
from the oxygen sensor installed to the exhaust
manifold and the engine operating condition
signals from other devices and sends out and
stops the electrical signal to the mixture control
solenoid valve to actuate the plunger up and
down 16 times every second. The ECM is locat-
ed under the glove box of the instrument panel.
4-6

l Since the mixture control solenoid valve is
factory adjusted, it must not be overhauled
or its jets must not be removed.
l Since the mixture adjust screw is also factory
adjusted, it must not be adjusted at the field
except the following.
a. When the carburetor assembly has been
replaced.
b. When the carburetor has been overhauled.
c. When the idle mixture adjustment is
necessary due to the emission test failures.
To adjust the mixture adjust screw in one of
the above conditions, drive out the pin in
front of the screw. After the adjustment, a
new pin should be installed.
1. Primary main jet
2. Primary slow jet
3.PrimaryslowairNo.2bleeder
4.PrimaryslowairNo.1bleeder
5. Mixture control solenoid valve
6. Idle down channel
7. Off idle discharge port8. Idle discharge hole
9.Plunger
10.Air jet
11. Mixture adjusting screw
12.Pin
13. Solenoid valve (Fuel cut)14. Economizer air bleeder
[Fuel cut system]
The primary slow system incorporates the fuel
cut system with the fuel cut solenoid valve
which is operated by the ignition switch and the
ECM. When the ignition switch is at “OFF”
position or during deceleration, the fuel cut
solenoid valve stops the fuel flow into the idle
down channel by closing the fuel passage. Thus
the fuel cut system helps to prevent the diesel-
ing and improve the emission performance and
fuel economy. For details, refer to SECTION 5
“EMISSION CONTROL SYSTEM”.
1.Fuel cut solenoid valve
2.Ignition switch
3.Battery4.Idle down channel5.Fuel passage6.Idle micro switch7.Primary main jet8.Thermal switch9.Ignition coil
10.ECM
Fig. 4- l-6 Fuel cut system
Fig. 4- 1-5 Primary slow system
4-7

[Primary main system1
The fuel metered by the primary main jet is mix-
ed with the air from the primary main air bleeder
and then is discharged into the carburetor bore
through the main discharge nozzle. When the
plunger of the MCS is at the up position (i.e. the
ECM electrical signal is not received by the
MCS), the fuel orifice of the MCS is open. In
this state, the fuel is allowed to flow into the
fuel passage through this orifice in addition to
the main jet and the mixture becomes rich.
On the other hand, when the plunger is at the
down position (i.e. the ECM signal is received by
the MCS), the fuel orifice is closed. In this state,
the fuel flows into the fuel passage only through
the main jet and therefore the mixture becomes
lean. In this way, the mixture is maintained to
the optimum air/fuel ratio at all times by the
plunger which moves up and down at a frequen-
cy of 16 times per second according to the
electrical,signals from the ECM.
1. Primary main jet2. Primary main air bleeder
3. Main discharge nozzle4. Mixture control solenoid valve
5.Plunger6.Fuel orifice
7.Fuelpassage
Fig. 4- 1-7 Primary main system
Secondary System
[Secondary slow system]
This system operates during the transition
period from the primary main system to the
secondary main system. When the primary
throttle valve is open nearly 54” and the vacuum
in “A” as shown in the below figure exceeds
specification, the diaphragm pulls up the rod.
In this state, the secondary throttle valve is
ready to open at any time when the primary
throttle valve opens further. When the secondary
throttle valve opens, the fuel discharged through
the secondary main jet is mixed with the air
from the economizer air bleeder at the secondary
slow jet. Then it is further blended with the air
from the secondary slow air bleeder and enters
into the carburetor bore through the idle down
channel.
1. Secondary main jet2. Economizer air bleeder
3. Secondary slow jet
4. Secondary throttle valve
5. Secondary slow air bleeder6. Idle down channel
Fig. 4-l-8 Secondary slow system
4-8

[Secondary main system]
Operation of the secondary throttle valve is also
controlled by the VTV and VSV. When the VSV
is closed, the vacuum to be applied to the
secondary diaphragm passes the VTV side and
the secondary throttle valve opens gradually.
When the primary throttle valve opens almost
fully, the VSV opens according to the signal
from the ECM. Then the vacuum is applied
directly to the secondary diaphragm and the
secondary throttle valve responds to intensity of
vacuum. When the secondary throttle valve open-
ing is wider than when secondary slow system
operates, the fuel is discharged through the
secondary main jet and mixed with the air from
the secondary main air bleeder. The air/fuel
mixture is discharged into the carburetor bore
through the main discharge hole.
1. Secondary main jet2. Secondary main air bleeder
3. Main discharge hole4. Primary throttle valve
5. Secondary throttle valve
6.Secondarydiaphragm7.VTV
8.VSV
Acceleration Pump System
This system operates to supply extra fuel to the
primary side only during the acceleration.
When the primary throttle valve closes, the
return spring pushes up the pump piston. Then
the fuel pushes up the check ball and enters into
the pump cylinder. When the throttle valve opens
during the acceleration, simultaneously the
pump piston is pushed down by means of the
pump lever. Then the fuel in the pump cylinder
pushes up the discharge ball and the lower
injector weight and discharges into the carbure-
tor bore from the pump discharge nozzle.
In this way, a higher acceleration performance is
provided by this system.
1. Primary throttle valve
2.Return spring3.Pump piston
4.Check ball6.Pump cylinder
6.Plunger7.Pump lever8.Discharge ball
9.Injector weight10. Pump discharge nozzle11. Pump damper spring
Fig. 4- l- 10Acceleration pump s ys tern
Fig. 4-l-9 Secondary main system
4-9

Choke System1) When coolant temperature is low:
This choke system is provided with a thermo-
wax which operates according to the heat from
the engine coolant, causing the choke valve to
open and close as well as the fast idle system to
operate automatically.
As the thermo-wax is contracted and the
plunger is retracted, the choke valve linked
with the fast idle cam is closed. When the
engine is started in this state, the intake
manifold vacuum pulls the diaphragm of the
choke piston to the left (below figure). The
choke piston rod also moves to the left and
acts on the choke valve to open. However,
the choke valve is restricted by the plunger of
the thermo-wax through the choke lever.
Therefore, the rod cannot move to the left
far enough to open the choke valve wide and
has .to stop at a position where the choke
valve opening is small as shown in the figure.
In this state, the diaphragm contracts the
bucking spring.
8
6
1.Choke piston2.Vacuum3.Therms wax
4.Plunger5. Fast idle cam
6.Cam follower7.Throttle valve8.Choke valve
Fig. 4- I- 11Choke system
[Operation of choke system]
As the thermo-wax is contracted at the low
coolant temperature, the plunger of the thermo-
wax is retracted (at the up position) and the fast
idle cam rotates clockwise by the spring force.
As a result, the cam follower pushed down by
the cam causes the primary throttle valve to
open and brings about the fast idle state.
The thermo-wax expands as the coolant tempe-
rature rises and the plunger position lowers,
causing the fast idle cam to rotate counterclock-
wise. As a result, the throttle valve starts moving
to close. In this way, the throttle valve closes
gradually as the coolant temperature rises until
it reaches the idling position at the normal
temperature. Refer to Fig. 4-l -11.
1.Choke piston
2.Intake manifoldvacuum
3.Diaphragm
4. Choke piston rod
5.Choke valve
6.Choke lever
7.Bucking spring
Fig. 4- I- 12 When coolant temp. is low
2) When the coolant temperature rises:
The plunger lowers due to the expansion of
the thermo-wax. Then the fast idle cam rotates
counterclockwise and consequently the choke
lever clockwise. This allow the rod to move
further to the left by the bucking spring force
(below figure). Thus a wide opening of the
choke valve is obtained.
Hereafter, the plunger of the thermo-wax
moves futher down in accordance with the
coolant temperature rise. The lower the
plunger moves, the wider the choke valve
opening becomes, and it becomes fully open
at the normal coolant temperature.
4-10

Fig. 4- l- 13 When coolant temp. rises
[Unloader system1
If accelerator pedal is depressed for acceleration
while the opening of the choke valve is small,
the throttle lever pulls down the unloader lever
and the choke valve opens up temporarily for
smooth acceleration.
1. Unloader lever
2. Choke valve
Fig. 4-1-14 Unloader system
Idle Up System
This system operates at idling and compensates
the idle speed;
1) When any one of following electric loads is
operating.
l Small light, tail light, side marker light &
license light
l Rear defogger (if equipped)
l Heater fan
2) When car is at a high altitude (higher than
1,220 m (4,000 ft) and HAC is ON).
3) When temperature in engine room is cold
(below 7°C (44°F) and thermal switch is
ON).
4) When engine speed after engine start is lower
than 1,500 r/min.
The ECM sends an electric signal to the Three
Way Solenoid Valve (TWSV). Receiving the
signal, the TWSV opens its inner valve and
transmits the manifold vacuum to the idle-up
diaphragm. As the diaphragm moves down by
the vacuum, the rod move down and push the
throttle lever to open the throttle valve a little
for the idle-up state.
In this way, the idle-up system helps to stabilize
the idle speed even when electric loads operate.
When electric loads stop operating, the TWSV
closes. Then the idle-up diaphragm as well as
rod moves back up, thus the idle-up state is
released.
I
5 1.
2.
3.
4.5.
8.
7.
8.
Idle-up actuatorAdjusting screw
Diaphragm
Rod
Throttle lever
Throttle valve
Twsv
To intake manifold
Fig. 4- I- 15 Idle-up system operation
4-11

REMOVAL AND INSTALLATION
Removal and installation of carburetor
place where no fire is used around.
Removal
1) Disconnect negative battery cord from
battery.
2) Drain coolant.
WARNING:
To help avoid the danger of being burned,
do not remove the drain plug and the
radiator cap while the engine and radiator
are still hot. Scalding fluid and steam can
be blown out under pressure if the plug
and cap are taken off too soon.
3) Remove air intake case from carburetor.
4) Disconnect micro switches, switch vent sole-
noid valve, fuel cut solenoid valve and MCSV
lead wires at their couplers.
5) Disconnect VSV coupler from VSV.
6) Detach bracket with EGR modulator and
TWSV from carburetor.
1. Bracket3.EGRmodulator2. Twsv
Fig. 4- 1-16
7) Disconnect water inlet and outlet hoses from
carburetor.
8) Disconnect accelerator cable from carburetor.
9) Disconnect vacuum hoses from idle up
actuator and carburetor.
10) To release the pressure in fuel tank, remove
fuel tank filler cap and then, reinstall it.
11) Disconnect fuel inlet hose from carburetor.
12) Check all around carburetor for any other
parts required to be removed or disconnect-
ed for removal of carburetor and remove or
disconnect whatever necessary.
13) Remove carburetor from intake manifold.
Fig. 4- 7- 17
Installation
Install in the reverse order of removal using care
for the following.
l Install carburetor to intake manifold.
Tighten 4 carburetor nuts to the specified
torque.
Tightening torque
for nuts13.5 - 20.0 lb-ft
l Connect water hoses to carburetor.
1. Carburetor
Fig. 4- I- 18
2. Inlet hose3. Outlet hose
4-12

0 Connect electric couplers securely.
l Connect accelerator cable to carburetor. With
the accelerator pedal released, adjust the cable
play to specification. This adjustment can be
made by turning the adjusting nut. After
adjustment, tighten the lock nut. Refer to
p. 4-19.
l Connect vacuum hoses securely.
l Refill cooling system.
l Connect negative cable at battery.
NOTE:
Upon completion of installation, be sure to
check each part for evidence of fuel leakage and
for proper operation. If defective, correct..
UNIT REPAIR OVERHAUL
This section outlines procedure to be used for
overhauling carburetor as removed from engine.
For removal and installation of carburetor from
and to engine, refer to the previous page.
NOTE:
l Be sure to replace gaskets as well as worn or
damaged parts.
l While disassembling and assembling carbure-
tor, use special care not to deform levers on
throttle valve shaft or cause damage to any
other parts.
l Don’t disassemble mixture control solenoid
valve and accelerator pump piston.
l Don’t remove idle and wide open micro
switches from the bracket where they are
installed.
Disassembly
1) Turn fast idle cam counterclockwise and
insert a pin avialable into holes on cam and
bracket to lock the cam.
Fig. 4- I- 19
1. Fast idle cam
2. Bracket3. Pin
4-13