WEBER CARBURETOR WITH GOVERNOR
c. Main Metering System
GENERAL
d. Power System
This section has the description and the service proce-
dures for the gasoline carburetor and governor that are
e. Accelerator Pump System
installed on the GM 4.3 litre V 6 and 5.7 litre V 8 en-
gines. A troubleshooting section is included at the end of
f. Choke System
this section.
Governor (See Figure 8)
DESCRIPTION
A governor is used to control the maximum speed of the
engine. The governor allows full power output for full
Carburetor (See FIGURE 1.)
engine load to very near the speed limit set by the gover-
The carburetor has two venturis, an accelerator pump
nor. An electronic controller and a solenoid valve con-
and an automatic choke. The arrangement of the carbu-
trol the operation of the governor.
retor is shown in FIGURE 1. There are six basic systems
of the carburetor. These systems control the mixing of
The governor is installed between the carburetor and the
the fuel with the air flow in the carburetor. The carbure- inlet manifold. The solenoid valve is installed on the
tor makes the correct air and fuel mixture for the differ- body of the governor. The governor controller is on the
ent operating conditions of the engine. The following
cowl in the operator s compartment. Vacuum lines con-
systems are described in this section:
nect the diaphragm of the governor to the solenoid valve
and the throttle body of the governor. The governor con-
a. Float System
troller is electrically connected to the solenoid valve and
b. Idle System the ignition distributor.
SIDE VIEW
TOP VIEW
TOP VIEW
1
7
10
11
6
5
1
2
12
5
3
8
4
8
9
1. AIR HORN 7. CHOKE LINKAGE
2. FLOAT BOWL 8. IDLE SOLENOID
3. THROTTLE PLATE HOUSING 9. VACUUM PORT FOR GOVERNOR
4. GOVERNOR 10. BRASS ORIFICE
5. GOVERNOR DIAPHRAGM HOUSING 11. BLACK ORIFICE
6. ACCELERATOR PUMP LINKAGE 12. SOLENOID VALVE
FIGURE 1. CARBURETOR WITH GOVERNOR
1
Additional air and fuel is necessary to increase the speed
OPERATION
of the engine. The volume of air is increased by opening
Carburetor, Float System (See FIGURE 2.) the throttle plate. The additional fuel comes from the
off idle port. As the throttle plate opens slowly, there is
The float system controls the level of the fuel that is in
now vacuum at the off idle port. Since there is vacuum
the float bowl. The float bowl receives fuel from the fuel
at both idle ports, the air and fuel mixture flows from
pump. As the fuel enters the float bowl, the float raises.
both ports.
When the level of the fuel is correct, the needle valve is
held against its seat and stops the flow of fuel. When the
5
level of the fuel lowers in the float bowl, the needle
6
valve moves from the seat. Fuel enters the float bowl
again until the level of the fuel is correct. This cycle con-
tinues during engine operation to keep a constant level
of fuel in the float bowl.
7
1
2
1
3
4
3
4
9 7
2
8
5 8
1. THROTTLE PLATE
2. FLOAT BOWL
11743
3. MAIN METERING JET
4. MAIN FUEL WELL
5. IDLE TUBE
11743
6. IDLE CHANNEL
1. FLOAT BOWL
7. OFF IDLE PORT
2. FLOAT 4. SEAT
8. IDLE PORT
3. NEEDLE 5. FUEL INLET
9. IDLE MIXTURE SCREW
FIGURE 2. THE FLOAT SYSTEM
FIGURE 3. THE IDLE SYSTEM
The float bowl has a vent that goes to the bore of the car-
A solenoid (see Figure 11) is installed on the carburetor.
buretor above the choke plate. This vent permits the air
The solenoid prevents the engine from continuing to run
pressure in the float bowl to be equal with the pressure of
when the ignition switch is in the OFF position. The so-
the flow of air through the carburetor.
lenoid is energized when the ignition switch is in the ON
position. A plunger extends from the solenoid and holds
Carburetor, Idle System (See FIGURE 3.)
the throttle shaft at the idle position. When the ignition
Each bore of the carburetor has its own idle system. At
switch is in the OFF position, the plunger retracts. The
idle speed, there is high vacuum at the idle ports because
throttle plate closes past the position for idle. This action
the throttle plate is only open a small amount. The vac-
restricts the flow of the air and fuel mixture that is neces-
uum at the idle ports causes fuel to flow from the float
sary to make the engine run.
bowl. The fuel then flows through the main metering
jets into the main fuel well. From the fuel well the fuel Carburetor, Main Metering System
(See FIGURE 4.)
goes up the idle tubes, mixes with the air and then flows
down the idle channels. The mixture in the idle channels The main metering system gives fuel to the engine from
flows to the idle ports. The air and fuel mixture now above idle speed to wide open throttle. As the throttle
flows into the carburetor bores. The idle mixture screws plates open, more air enters the engine and engine speed
control the amount of fuel mixture that enters each car- increases. With the increase in the throttle opening,
buretor bore. During idle, the position of the throttle there is also an increase in air velocity through the ven-
plate controls the idle speed of the engine. turis. The increase in air velocity causes a high vacuum
2
in the secondary venturis. The fuel mixes with air in the
3
main well tubes and flows to the main nozzle. From the
main nozzle and secondary venturi the fuel mixture en-
ters the inlet manifold.
1
4
4
6
3
1
5
11778
2
11778
2
1. THROTTLE PLATE
2. IDLE PORTS 1. POWER PISTON AND SPRING
3. SECONDARY VENTURI 2. POWER VALVE
5
4. MAIN NOZZLE 3. POWER CHANNEL
5. MAIN METERING JET 4. MAIN METERING JET
5. TO POWER TUBE (SEE
6. MAIN WELL TUBE
FIGURE 13. FOR DETAIL
FIGURE 4. MAIN METERING SYSTEM
FIGURE 5. POWER SYSTEM
Carburetor, Accelerator Pump System
Carburetor, Power System (See FIGURE 5.)
(See FIGURE 6.)
The power system gives more fuel through the main me- The accelerator pump is actuated by the throttle linkage
tering system during heavy load and acceleration condi- and gives additional fuel to the engine during quick ac-
tions of the engine. The power system has a power pis- celeration. When the throttle plates open quickly for ac-
ton and spring and a power valve assembly. Under nor- celeration, the air flow through the carburetor increases
mal conditions, the power piston is held closed by vac- immediately. Since the fuel is heavier than air, there is a
uum. Increasing the load on the engine lowers the mani- short delay before the fuel flows from the main nozzle.
fold vacuum. The decrease in vacuum causes the power When the throttle pedal is depressed quickly, the
piston to move down and open the power valve. The plunger for the accelerator pump pushes fuel from the
power valve permits additional fuel to flow to the main float bowl. The fuel flows along a passage and moves
metering jets for more engine power. through a check ball. Then the fuel enters into the ven-
3
turi. This action gives smooth engine operation during
1
acceleration.
2
3
6
4
2
5
1
ÂÂ
ÂÂ
4
11746
3
5
7
11743
1. FLOAT BOWL
2. ACCELERATOR PUMP
1. THERMOSTATIC COIL
3. FUEL PASSAGE
2. CHOKE PLATE SHAFT
4. CHECK BALL
3. CHOKE PISTON
5. OUTLET TO THROTTLE BORE
4. VACUUM PASSAGE
6. LINK TO THROTTLE LINKAGE
5. TUBE IN INLET MANIFOLD
7. SCREEN
FIGURE 7. CHOKE SYSTEM
FIGURE 6. ACCELERATOR PUMP SYSTEM
Carburetor, Choke System
2
The choke system helps start and keep running an en-
3
gine that is cold. To start a cold engine, the throttle pedal
is pushed to set the fast idle cam and close the choke
plate. The choke plate is held closed by the thermostatic
coil when the engine is cold. When the engine is started,
air velocity causes the choke plate to open against the
1
torque of the thermostatic coil. In addition, vacuum
from the inlet manifold is applied to the choke piston.
This action causes the choke piston to help open the
choke plate. Any acceleration or increase in engine load
decreases the vacuum on the choke piston. The thermos-
tatic coil can close the choke plate to increase the fuel to
air ratio for acceleration.
4
1. ELECTRIC HEATER
As the engine warms up, hot air is drawn through the
11754
2. CHOKE COVER
tube in the inlet manifold and into the choke housing.
3. ELECTRICAL CONNECTION
(See FIGURE 7.) The hot air removes the tension from
4. CHOKE TUBE
the thermostatic coil and the choke plate opens. The fast
FIGURE 8. ELECTRIC CHOKE
idle cam holds the throttle plate open enough to increase
ARRANGEMENT
engine speed until the choke plate opens fully.
4
NOTE: An electric choke conversion kit was made in the circuit for the controller. When the engine speed
available for the GM V 6 engine in 1992. See signal is more than the internal reference, current flows
FIGURE 8. This conversion disconnects the heat tube to the solenoid valve. The solenoid valve closes, causing
from the inlet manifold and uses an electric heater coil to manifold vacuum to operate the diaphragm. When actu-
heat the thermostatic coil of the choke control. This con- ated, the diaphragm works against the governor spring
version kit improves the starting of the engine and the to close the throttle plates and decrease engine speed.
idle speed during cold temperatures. The operation of The solenoid valve opens and closes as necessary to
the choke system is not changed from the description. keep the engine speed within the limits of the governor.
GOVERNOR (See FIGURE 9.)
CLEAR
The operation of the governor is controlled by an elec-
RED
tronic controller. Manifold vacuum provides the force to
BARE
BRN
actuate the governor while the controller regulates this
BLK
force. The governor has two throttle plates that are con-
nected to a diaphragm. Linkage from the diaphragm
closes the throttle plates. A spring in the governor opens
RED
2
the throttle plates. (The throttle linkage is not connected
to governor throttle plates.)
3
1
1. BLACK ORIFICE
2. BRASS ORIFICE TO
VACUUM PORT OF
1. DISTRIBUTOR
GOVERNOR
2. GOVERNOR CONTROLLER
3. DIAPHRAGM
5
1 3. SOLENOID VALVE
11719
4. DIAPHRAGM ROD
2
5. VACUUM CHAMBER
FIGURE 10. GOVERNOR CIRCUIT
6. GOVERNOR LEVER
7. GOVERNOR SPRING
7
3
3
4
6
11718
1
FIGURE 9. GOVERNOR
The electronic controller is connected to the distributor
and controls the operation of the solenoid valve. The so-
4
lenoid valve controls the vacuum at the diaphragm in the
1. PORT TO AIR CLEANER
governor. When the solenoid valve is not energized, it is
2
2. PORT TO GOVERNOR
open and manifold vacuum does not affect the governor.
4
3. SOLENOID VALVE
During operation, the electronic controller receives en-
4. ELECTRICAL CONNECTION
gine speed (rpm) signals from the distributor. The con-
FIGURE 11. GOVERNOR SOLENOID VALVE
troller compares these signals with an internal reference
5
REPAIRS
Use a fluid for cleaning carburetors to clean the carbure-
CARBURETOR
tor. Use compressed air to clean the passages that are in-
Removal
side of the carburetor.
WARNING
CAUTION
Keep all fire and sparks away from the area of re-
Do not use wire or a drill to clean the jets or the pas-
moval and disassembly. To prevent electrical sparks,
sages of the carburetor.
disconnect the ground cable at the battery.
1. Close the valve in the fuel line. Disconnect the fuel
line from the carburetor. Let the gas drain from the line.
Assembly
(See FIGURE 1.Through FIGURE 7.)
Make sure to put a cap on the open line.
2. Disconnect the air cleaner. Disconnect the vacuum
1. Use a new gasket and install the throttle plate housing
lines at the carburetor.
on the float bowl housing.
3. Disconnect the throttle linkage and the wire at the idle
2. Install the power jet and main jets in the float bowl.
solenoid. Disconnect the tube from the choke assembly.
Install the main discharge nozzle.
4. Remove the nuts that hold the carburetor to the gover-
nor. Remove the carburetor.
3. Install the accelerator pump on the lever. Make sure
the retainer clip is toward the inside of the carburetor.
Disassembly
(See FIGURE 1.Through FIGURE 7.)
4. Install the gasket for the air horn. Install the needle
CAUTION and float. Adjust the float level (see FIGURE 12.) as fol-
lows:
Do not remove the throttle plates, the choke plate or
the shafts unless they are damaged.
a. The air horn upside down. Measure the distance
1. Disconnect the choke linkage. Remove the screws
from the gasket to the joint in the float. The cor-
that hold the air horn to the float bowl housing. Remove
rect distance is 12.7 mm (0.50 in). Bend the float
the air horn.
arm to change the adjustment.
2. Remove the float, needle and accelerator pump. Make
b. Hold the air horn in the normal position. Measure
a note of how the accelerator pump is connected to the
the distance from the gasket to the joint in the
lever in the air horn.
float. The correct distance is 44.5 mm (1.75 in).
3. Remove the screws that hold the throttle plate housing
Bend the float arm to change the adjustment.
to the float bowl housing. Remove the throttle plate
housing.
5. Install the spring for the accelerator pump in the float
bowl housing. Install the air horn, making sure the ac-
4. Remove the jets from the float bowl. Remove the
celerator pump fits in the housing. The link between the
main discharge nozzle assembly. Remove the adjust-
choke plate and the throttle linkage must be installed
ment screws from the float bowl housing.
when the air horn is installed.
5. Remove the choke assembly and the fuel screen from
the air horn.
6. Install the thermostatic coil and gasket in the housing.
Make sure the coil engages with the choke plate. Turn
Cleaning
the cover for the coil so that the marks are aligned. (See
WARNING Checks and Adjustments.)
The fluid for cleaning carburetors is very flamma-
7. Install the screen in the inlet fitting. Install the adjust-
ble. Carefully follow the instructions of the manufac-
ment screws.
turer.
6
3
1
44.5 mm
(1.75 in)
2
12.7 mm
3
(0.50 in)
2
1. AIR HORN
2. FLOAT
1
3. BEND HERE TO ADJUST
FIGURE 12. FLOAT ADJUSTMENT
Installation 6. Make sure the screen is in the inlet fitting that fits be-
tween the carburetor and the air filter. Connect the air
1. See FIGURE 13. Install the tube and the O ring that
filter to the carburetor.
fits between the governor and the carburetor.
GOVERNOR (See FIGURE 9.)
2. Use a new gasket and install the carburetor on the gov-
If the governor is not operating correctly, check the parts
ernor.
of the system as follows:
3. Connect the fuel line to the carburetor. Connect the
1. Check the vacuum hoses and the diaphragm in the
wire to the solenoid.
governor for damage. Remove the plate on the side of
the governor and check that the linkage and spring move
4. Connect the heat tubes for the choke assembly. Make
freely.
sure the connections at the carburetor are tight. Make
sure the tubes are completely installed in the fittings in
NOTE: The vacuum hoses installed on the carburetor
the inlet manifold. (See FIGURE 7.)
and governor are made of special high temperature ma-
terial. If any of the hoses are replaced, make sure the cor-
rect hoses are installed.
2. Check the vacuum hoses for restrictions. Check the
tee fitting at the diaphragm for restrictions. Make sure
the tee fitting is correctly installed. There are orifices in
3
the fitting. The black ( VAL ) side is for the solenoid
1
valve. The brass ( GOV ) side is for the governor.
2
3. Use an ohmmeter to check the solenoid valve. Dis-
connect the wire at the solenoid valve. Measure the re-
4
sistance between the terminals of the solenoid valve.
1. CARBURETOR
The correct resistance is 25 35 ohms. Measure the resis-
2. GOVERNOR
tance between one of the terminals and the body of the
3. TUBE
4. O RING
solenoid valve. The correct resistance is 800 ohms or
higher. If the readings are not correct, replace the sole-
FIGURE 13. TUBE FOR POWER CIRCUIT
noid valve. If the solenoid valve is defective, the gover-
nor controller must also be checked. A defective sole-
noid valve can damage the electronic controller.
5. Connect the linkage for the throttle. Adjust the carbu-
retor as described in Checks and Adjustments. 4. Use a volt/ohmmeter to check the governor controller.
7
a. Disconnect the wiring harness at the controller. Check for defective wires if the readings are not
Measure the resistance between the ground ter- correct.
minal in the harness connector and the cowl. The
c. Turn the key switch to the OFF position. Use an
correct resistance is less than 3 ohms. If the cir-
ohmmeter to check the continuity of the signal in-
cuit is open or the resistance is high, check for a
put wire (black). Check the wire between the dis-
defective wire. Correct the problem before doing
tributor (tachometer connector) and the harness
step 2.
connector.
b. Turn the key switch to the ON position. (Do not
start the engine.) Use the voltmeter to check for 5. If, after checking the solenoid valve, wiring, hoses
battery voltage at the terminals in the connector and the governor, the governor does not operate cor-
for the battery (red) and the solenoid (yellow). rectly, replace the electronic controller.
CHECKS AND ADJUSTMENTS
GENERAL
Before making any adjustments, check that the nuts for
the carburetor and governor are tight. Make sure there
are no air leaks.
Check that the vacuum hoses for the governor are con-
nected and do not leak. Make sure the heat tubes for the
choke are connected and do not leak.
Connect a tachometer to the engine.
1. ALIGNMENT MARKS
CHOKE SYSTEM (See FIGURE 14.) 11754
2. CHOKE COVER
3. IDLE MIXTURE SCREW
FIGURE 14. CHOKE ARRANGEMENT
1. Align the mark on the choke cover with the mark on
the housing. If necessary, rotate the choke cover to align
ELECTRIC CHOKE (See FIGURE 15.)
the marks.
1. Align the mark on the choke cover with the mark on
the housing. If necessary, rotate the choke cover to align
2. Depress the throttle pedal to the floor and release it to
the marks.
the low idle position. When the engine is cold, check
that the choke plate is fully closed. 2. Depress the throttle pedal to the floor and hold it in
that position. Check that the choke plate is open a small
amount.
3. Depress the throttle pedal to the floor and hold it in
this position. Check that the choke plate is open a small 3. Start the engine and run at idle speed. The choke will
amount. correctly be fully open in 2 to 4 minutes. Fine adjust-
8
ments of the choke control can be made for the best posi- to the right until the idle speed decreases and the
tion to start the engine and run at idle speed. Turn the engine begins to run rough.
choke cover counterclockwise to increase the fuel in the
c. Turn the screw to the left to a point between the
mixture (rich). Turn the choke cover clockwise to de-
rich and lean limits to get (1) highest idle speed,
crease the fuel in the mixture (lean).
(2) highest manifold vacuum and (3) smoothest
engine operation.
2
3
4. Adjust the other idle mixture screw as described in
step 3.
5. If necessary, adjust the idle speed to 600 rpm as de-
scribed in step 2.
6. Adjust both idle mixture screws as described in steps
1
3 and 4.
IDLE SPEED ADJUSTMENT
(See FIGURE 16.)
1. Start the engine. With the idle solenoid energized
3
(stem extended), adjust the stem of the solenoid to get an
1. ALIGNMENT MARKS
11754
2. CHOKE COVER idle speed of 650 rpm.
3. ELECTRICAL CONNECTION
4. IDLE MIXTURE SCREW
2. Start the engine and disconnect the wire at the idle so-
lenoid. Make sure the choke plate is fully open and the
FIGURE 15. ELECTRIC CHOKE
fast idle cam is rotated fully clockwise. Turn the idle
ARRANGEMENT
speed screw to get an idle speed of 400 rpm. Connect the
wire to the idle solenoid and check that the normal idle
IDLE MIXTURE ADJUSTMENT
speed is 650 rpm.
(See FIGURE 14.)
1. Run the engine until it reaches the normal operating
4
temperature.
5
WARNING
Be careful of the fan and drive belts when the engine
3
is running.
2. Adjust the idle speed to 600 rpm by adjusting the stem
of the idle solenoid. (See FIGURE 16.) (Make sure the
solenoid is energized.)
2
1
3. Adjust one of the idle mixture screws as follows:
11754
1. IDLE SOLENOID
a. Turn the screw to the left (rich mixture) until the
2. SOLENOID STEM
3. SOLENOID WIRE
idle speed decreases and the engine begins to run
4. LINK TO CHOKE PLATE
rough.
5. IDLE SPEED SCREW
b. Turn the screw to the right (lean mixture) until the
FIGURE 16. IDLE SPEED ADJUSTMENT
idle speed increases. Continue to turn the screw
9
3. Depress the throttle pedal until it stops against the
THROTTLE LINKAGE ADJUSTMENT
floor plate. Adjust the throttle cable so that the pedal
(See FIGURE 17.)
stops on the floor plate as the throttle plates reach the
1. Adjust the idle speed as described in Idle Speed Ad- wide open position. Use the cable adjustment nuts on the
justment.
cable housing to change the adjustment of the cable.
2. Make sure the throttle linkage at the pedal assembly is 4. Adjust the pedal stop so that the pedal and throttle
in the correct position as shown in FIGURE 17. lever reach the full return positions at the same time.
1. LINKAGE FOR GAS CARBURETOR
2. THROTTLE CABLE
6
3. CABLE ADJUSTMENT NUTS
1
3
4. PEDAL ASSEMBLY
5. PEDAL STOP
6. RETURN SPRING
3
2
4
5
11724
FIGURE 17. THROTTLE LINKAGE ADJUSTMENT
10
TROUBLESHOOTING
PROBLEM POSSIBLE CAUSE
The engine will not start or the engine is difficult to The vent in the fuel cap has a restriction.
start.
The air filter has a restriction.
The fuel lines or the fuel screen has a restriction.
The shut off valve at the fuel tank is closed.
The choke does not operate correctly.
The carburetor is not adjusted correctly.
The fuel pump does not operate.
The smoke from the exhaust is black. The choke does not open completely.
The electric choke is bad or does not have electric
power.
Power piston, or O ring, or power tube is
damaged.
The adjustment of the carburetor is not correct.
The needle valve for the float will not close.
The engine does not idle smoothly. The adjustment for idle mixture is not correct.
The carburetor has air leaks.
The idle passages have restrictions.
The height of the float is not correct.
The needle valve for the float is worn.
The carburetor or governor has air leaks or cracks.
The gaskets are damaged.
The engine runs after it is shut off. The idle solenoid has a defect or is not adjusted
correctly.
The choke linkage does not operate correctly.
The ignition timing is not correct.
The speed of the engine does not increase smoothly. The fuel screen in the fuel line has a restriction.
The operation of the accelerator pump is not correct.
The height of the float is not correct.
The air filter has a restriction.
Power piston, or O ring, or power tube is
damaged.
The choke does not open completely.
The carburetor has air leaks.
The vacuum lines for the governor are not connected.
The operation of the governor, controller or solenoid
valve is not correct.
11