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FUEL SYSTEM/CARBURETOR/FUEL PUMP
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SCHEMATIC DRAWING ---------------------------------------------- 13- 1
SERVICE INFORMATION -------------------------------------------- 13- 4
TROUBLESHOOTING ------------------------------------------------- 13- 4
CARBURETOR REMOVAL ------------------------------------------- 13- 6
VACUUM CHAMBER DISASSEMBLY------------------------------ 13- 6
FLOAT CHAMBER DISASSEMBLY--------------------------------- 13- 8
AUTO BYSTARTER INSPECTION/REMOVAL-------------------- 13-10
AIR CUT-OFF VALVE (A.C.V.)-------------------------------------- 13-11
AUTO BYSTARTER INSTALLATION ------------------------------ 13-13
FLOAT CHAMBER ASSEMBLY ------------------------------------- 13-14
FLOAT LEVEL INSPECTION ---------------------------------------- 13-15
VACUUM CHAMBER ASSEMBLY ---------------------------------- 13-15
CARBURETOR INSTALLATION ------------------------------------ 13-16
FUEL PUMP REMOVAL/DISASSEMBLY -------------------------- 13-17
FUEL PUMP INSPECTION-------------------------------------------- 13-18
FUEL PUMP ASSEMBLY --------------------------------------------- 13-18
FUEL PUMP INSTALLATION --------------------------------------- 13-19
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FUEL SYSTEM
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SCHEMATIC DRAWING
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FUEL PUMP
CONSTRUCTION:
The fuel pump adopted for this model is a vacuum-type fuel pump which utilizes the positive and
negative pulsating pressures produced by the engine crankcase to control the oil pump diaphragms
and deliver fuel from the fuel tank to the carburetor through the suction valve and outlet valve.
FUEL PUMP CONSTRUCTION
Diaphragms
Inlet
Outlet
Suction Valve
Outlet Valve
Pulsating Pressure
from Crankcase
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SERVICE INFORMATION
GENERAL INSTRUCTIONS
• When working with gasoline, keep away from sparks and flames.
• Note the locations of O-rings when disassembling and replace them with new ones during
assembly.
• Before float chamber disassembly, drain the residual gasoline from the float chamber.
• Do not try to disassemble the auto bystarter.
• When assembling the vacuum chamber and air cut-off valve, be careful not to damage the
diaphragms.
• All cables, fuel lines and wires must be routed and secured at correct locations.
SPECIFICATIONS
Venturi dia. (mm)
VE26
Identification number
VE090
Float level (mm)
18.5
Pilot screw opening
2±_
Main jet
102#
Slow jet
35#
Idle speed
1600±100rpm
Fuel pump output
40cc/1600rpm/10 seconds
SPECIAL TOOLS
Float level gauge
Fuel unit remover
TROUBLESHOOTING
Engine does not start Engine idles roughly, stalls or runs poorly
• No fuel in tank • Incorrect idle speed
• Restricted fuel line • Rich mixture
• Too much fuel getting to cylinder • Lean mixture
• Clogged air cleaner • Clogged air cleaner
• Contaminated fuel • Intake air leak
• Faulty fuel pump • Contaminated fuel
• Faulty air-cut off valve
• Damaged vacuum tube and connectors
• Damaged carburetor insulator
B
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Throttle does not open fully, so engine stalls Rich mixture
• Damaged vacuum piston diaphragm • Auto bystarter valve opens excessively
• Clogged diaphragm hole • Faulty float valve
• Float level too high
Lean mixture • Clogged air jets
• Clogged fuel jets • Auto bystarter valve set plate installed in
• Clogged fuel tank cap breather hole
the wrong groove
• Clogged fuel filter •Clogged air cleaner
• Bent, kinked or restricted fuel line
• Faulty float valve
• Float level too low
• Faulty fuel pump or insufficient output
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CARBURETOR REMOVAL
Remove the seat, met-in box and center
cover.
Disconnect the fuel tube and vacuum tube at
the carburetor.
Disconnect the auto bystarter wire.
Loosen the throttle cable adjusting nut and
lock nut, and disconnect the throttle cable
from the carburetor.
Loosen the air cleaner connecting tube band
and carburetor intake manifold band and then
remove the carburetor.
VACUUM CHAMBER
DISASSEMBLY
Loosen the drain screw and drain the fuel
from the float chamber.
Auto Bystarter Wire
Auto Bystarter
Fuel Tube
Intake Manifold Band
Air Cleaner Connecting Tube Band
Drain Screw
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Remove the two vacuum chamber cover
screws and the cover.
Remove the compression spring and vacuum
piston.
Remove the needle holder, spring and jet
needle from the piston.
VACUUM PISTON INSPECTION
Inspect the vacuum piston and jet needle for
wear or damage.
Inspect the diaphragm for deterioration and
tears.
Vacuum Chamber Cover
Diaphragm
Screws
Spring
Spring
• Be careful not to damage the vacuum
piston diaphragm.
＊
Vacuum Piston
Vacuum Piston
Needle Holder
Jet Needle
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FLOAT CHAMBER DISASSEMBLY
Remove the four float chamber screws and
the float chamber.
Remove the float pin, float and float valve.
FLOAT VALVE INSPECTION
Inspect the float valve seat contact area for
wear.
Float Chamber
Float Valve
Float
Float Pin
Float Valve Seat
Screws
Float Valve
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JETS/SCREWS REMOVAL
Remove the main jet, needle jet holder and
needle jet.
Remove the slow jet.
Clean the removed the main jet, needle jet
holder, needle jet and slow jet with detergent
oil.
Pilot Screw (P.S.)
Pilot Screw
Slow Jet
• Be sure to use clean detergent oil.
＊
Main Jet
Needle Jet Holder
• Before removing the pilot screw, turn
the pilot screw clockwise until it seats
lightly and record the rotating turns.
Do not force the pilot screw against its
seat to avoid seat damage.
＊
Needle Jet Holder
Slow Jet
Main Jet
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AUTO BYSTARTER INSPECTION
/REMOVAL
AUTO BYSTARTER INSPECTION
Measure the resistance between the auto
bystarter wire terminals.
Resistance: 10Ω (10 minutes minimum
after stopping the engine)
If the reading is not within the limit, replace
the auto bystarter with a new one.
Connect a hose to the fuel enriching circuit
of the carburetor. Connect the auto
bystarter yellow wire to the positive (+)
terminal of a battery and green wire to the
negative (-) terminal. Wait 5 minutes and
blow the hose with mouth. If the passage is
blocked, the auto bystarter is normal.
Disconnect the auto bystarter from the
battery. Wait 30 minutes and blow the hose
with mouth.. If air can be blown into the
hose, the auto bystarter is normal.
AUTO BYSTARTER REMOVAL
Remove the two set plate screws and set
plate and then remove the auto bystarter
from the carburetor body.
Auto Bystarter
Screws
Set Plate
Hose
Yellow
Green
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AUTO BYSTARTER INSPECTION
Check the auto bystarter valve and needle
for nicks, wear or damage.
If any faulty part is found, replace the auto
bystarter with a new one.
AIR CUT-OFF VALVE (A.C.V.)
A.C.V. REMOVAL
Remove the two screws and the air cut-off
valve cover.
Remove the spring, diaphragm and O-rings.
Inspect the diaphragm and spring for wear or
damage.
Bystarter Needle
Air Cut-off Valve Cover
Bystarter Valve
Spring
Screws
Cover
Diaphragm
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Disconnect the hose at the valve seat.
Remove the two screws and the air cut-off
valve body.
CARBURETOR BODY CLEANING
Blow compressed air through all passages of
the carburetor body.
A.C.V. ASSEMBLY
Install the O-ring onto the air-cut-off valve
body and then install the valve body to the
carburetor with the two screws.
Hose
O-ring
Air Cut-off Valve Body
• Make sure that no fuel jet is clogged.
＊
• Install the O-ring with the flat face
toward the valve body side.
＊
Air Cut-off Valve Body
Screws
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Install the O-ring onto the air-cut-off valve
body securely.
Install the diaphragm, spring, and cover.
Install and tighten the two screws attaching
the air cut-off valve cover.
Connect the hose.
AUTO BYSTARTER INSTALLATION
Install the auto bystarter and set plate.
Install and tighten the two screws.
Auto Bystarter
Screws
• Install the O-ring with the flat face
toward the valve body side.
＊
Spring
Cover
Diaphragm
O-ring
Screws
Set Plate
• Insert the auto bystarter into the
carburetor body until it bottoms and
position the set plate into the upper
groove in the bystarter.
• Install the set plate with its round face
facing down.
＊
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FLOAT CHAMBER ASSEMBLY
Install the needle jet and needle jet holder.
Install the main jet.
Install the slow jet.
Install the pilot screw.
Install the float valve, float and float pin.
Float Valve
Float
Float Pin
Pilot Screw
Needle Jet Holder
Slow Jet Holder
Main Jet Holder
• Be sure to record the rotating turns
when it is removed.
＊
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FLOAT LEVEL INSPECTION
Measure the float level at the location of the
main jet (just contacting the float valve).
Float Level: 18.5±1.0mm
Replace the float if the level is incorrect.
Check the operation of the float and then
reinstall the float chamber.
VACUUM CHAMBER ASSEMBLY
First install the jet needle and spring into the
vacuum chamber and then install the needle
holder.
Install the vacuum piston into the carburetor
body.
Install the spring.
Diaphragm
Float
Spring
Vacuum Piston
• Align the hole in the diaphragm with
the vacuum passage in the carburetor
body.
＊
Diaphragm
Spring
Vacuum Piston
Needle Holder
Jet Needle
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Install the vacuum chamber cover and tighten
it with the two screws.
CARBURETOR INSTALLATION
Tighten the drain screw.
Install the carburetor onto the intake
manifold and tighten the band.
Install the air cleaner connecting tube and
tighten the band.
Connect the throttle cable to the carburetor.
Connect the auto bystarter wire.
Connect the fuel tube and vacuum tube to
the carburetor.
Perform the following inspections and
adjustments:
•Throttle grip free play (3-3)
•Idle speed (3-6)
Install the seat, met-in box and frame center
cover.
Auto Bystarter Wire
• Be careful not to let the diaphragm slip.
• If the diaphragm cannot be positioned
correctly because of expansion, dry the
diaphragm before installation.
＊
Vacuum Chamber Cover
Fuel Tube
Intake Manifold Band
Air Cleaner Connecting
Tube Band
Screws
• After connecting the throttle cable,
adjust the throttle grip free play to
2_ 6mm.
＊
Throttle Cable
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FUEL PUMP REMOVAL
Remove the frame center cover.
Disconnect the fuel pump inlet, outlet and
vacuum tubes.
Remove the fuel pump attaching two bolts
and the fuel pump.
FUEL PUMP INSTALLATION
Install the fuel pump and secure it with the
two bolts.
Connect the fuel pump inlet, outlet and
vacuum tubes.
Install the seat, met-in box and frame center
cover.
Measure the fuel pump output.
Start the engine and disconnect the fuel
outlet tube and place a clean container under
the tube to check the fuel output.
Output: 40cc/1500rpm/10 seconds .
Container
Fuel Pump
Fuel Pump
Outlet Tube
Fuel Strainer
Outlet Tube
Vacuum Tube
Inlet Tube
Outlet Tube
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FUEL STRAINER REMOVAL
Remove the fuel strainer from the inlet tube.
INSPECTION
Inspect if the fuel strainer is clogged and
clean it with compressed air.
INSTALLATION
Install the fuel strainer with its arrow mark
toward the fuel pump.
• When removing the fuel strainer, do not
allow flames or sparks near the
working area and drain the residual
gasoline into a container.
＊
Fuel Strainer
Arrow Mark
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