4. FUEL SYSTEM

Page 4-0


really big verson

Page 4-1

Service Information4-1
Troubleshooting4-2
Fuel tank4-3
Air cleaner case4-4
Carburetor removal4-5
Carburetor disassembly4-5
Pilot screw removal4-7
Carburetor assembly4-9
Carburetor separation/assembly4-12
Carburetor installation4-14
Pilot screw adjustment4-14
High altitude adjustment
(U.S.A. only)
4-15
Purge control valve inspection
(California model only)
4-16
Air vent control valve
(California model only)
4-17
Secondary air supply system
(California model only)
4-18

SERVICE INFORMATION

WARNING

General

CAUTION

NOTE

SPECIFICATIONS

'88After '88
Item49 St. ModelCalifornia model49 St. ModelCalifornia model
TypeConstant Velocity dual carburetor
Throttle bore36.5mm (1.4 in)
Identification No.VDGKAVDGLAVDGKAVDGLA
Float Level9.2mm (0.36 in)
Main jetFront: #138, Rear: #132
Slow jet#42
Idle Speed1,200 +/- 100 rpm
Throttle grip free play2-6 mm (1/8-1/4 in)
Pilot screw initial opening2-1/82-1/2Front:1-1/2, Rear: 11-3/8

Page 4-2

TORQUE VALUES

Fuel tank mounting bolt:Front12 N.m (1.2 kg-m, 9 ft-lb)
:Rear22 N.m (2.2 kg-m, 16 ft-lb)

TOOLS

Special
Vacuum/Pressure pumpA937X-041-XXXXX or
   Pressure pumpST-AH-255-MC7 (U.S.A. only)
   Vacuum pumpST-AH-260-MC7 (U.S.A. only)
Common
Float level gauge07401-0010000

TROUBLESHOOTING

Engine cranks but won't start

Hard starting or stalling after starting

Rough idle

Afterburning during deceleration

Misfiring during acceleration

Backfiring

Poor performance (drivability) and poor fuel economy

Lean mixture

Rich mixture



Page 4-3


FUEL TANK

REMOVAL

WARNING

Remove the seat (page 3-25) and turn the fuel valve OFF.
Disconnect the fuel tube from the fuel tank.

'88 Only:
California model only:

Disconnect the No. 1 fuel breather tube (to canister) from the fuel tank.

All models:
Remove the rear fuel tank mounting bolt first, then the front bolt and remove the tank from the frame.

CAUTION

Check that fuel flows out of the fuel valve freely.
If flow is restricted, clean the fuel strainer.

After '88:
Remove the rear fuel tank mounting bolt first, then the front bolt.

Screw the rear mounting bolt in the front mounting collar.
Remove the rear mounting bolt and the collar as a set.

California model only:
Disconnect the No. 1 fuel breather tube (to canister) from the fuel tank.

All models:
Remove the fuel tank from the frame.

INSTALLATION

'88, After'88:
Install the fuel tank in the frame.
Install the front mounting collar and the bolt first, then the rear mounting bolt.

TORQUE:
   Front: 12 N.m (1.2 kg-m, 9 ft-lb)
   Rear: 22 N m (2.2 kg-m, 16 ft-lb}

Connect the removed tubes securely.

Page 4-4


AIR CLEANER CASE

REMOVAL

NOTE

Remove the seat and fuel tank.
Remove the air cleaner case mounting bolt.

Loosen the air cleaner connecting tube band screws and disconnect the crankcase breather and air cleaner case drain tube.
Remove the air cleaner case.

Install the air cleaner case in the reverse order of removal.

SUB-AIR CLEANER ELEMENT

Remove the following: Disconnect the air hoses (carburetors-to-sub-air cleaner cover).
Remove the sub-air cleaner mounting bolt and cover and remove the element.

Wash the element in non-flammable or high flash point solvent, squeeze out the solvent thoroughly, and allow the element to dry.
Soak the element in gear oil (SAE #80 - 90) and squeeze out the excess.
Reinstall the element and cover, and tighten the bolt.
Reconnect the air tubes from the carburetors.

Page 4-5


CARBURETOR REMOVAL

WARNING

Loosen the drain screws and drain the fuel into a container.
Remove the air cleaner case.
Disconnect the throttle cables from the carburetor.

NOTE

Remove the choke valves from the carburetor and loosen the carburetor insulator bands.

California model only:
Disconnect the purge control valve No. 5 tubes and air vent control valve No. 6 and 11 tubes from the carburetor.

Pull the carburetors upward and away from the engine.

CARBURETOR DISASSEMBLY

NOTE

Remove the fuel tube from the carburetor.

VACUUM CHAMBER

Remove the four screws and vacuum chamber cover.

Page 4-6

Remove the spring, piston/diaphragm.
Inspect the vacuum piston for wear, nicks, scratches or other damage.

Make sure the piston moves up and down freely in the chamber.

Push the jet needle holder in and turn it in 90 degrees counterclockwise.

Then remove the needle holder, spring, jet needle and from the piston.
Inspect the needle for excessive wear at the tip, bending or other damge.
Inspect the diaphragm for damage, fatigue or pin holes.
Inspect the vacuum piston for wear or damage.

 

FLOAT CHAMBER, FLOAT AND JETS

Remove the four screws and float chamber.

Page 4-7

Remove the float pin, float and float valves.

Check the float valve and valve seat for scratches, clogging or damage.

Inspect the operation of the float valve.

Remove the main jet, needle jet, slow jet and valve seat/filter.

Check each part for wear or damage.
Blow open all jets with compressed air.

Clean each jet with non-flammable or high flash point solvent.

Inspect the float valve seat and filter for grooves, nicks or deposits.

Clean the filter with low-pressure compressed air.

PILOT SCREW REMOVAL

NOTE


Page 4-8


Center punch the pilot screw plug to center the drill point.
Drill through the plug with a 4 mm (5/32 in) drill bit. Attach a drill stop to the bit 3 mm (1/8 in) from the end to prevent drilling into the pilot screw.

CAUTION



Force a self-tapping 4 mm screw, P/N 93903 - 35410) into the drilled plug and continue turning the screwdriver until the plug rotates with the screw.

Pull on the screw head with pliers to remove the plug.

Use compressed air to clean the pilot screw area and remove metal shavings.
Turn each pilot screw in and carefully count the number of turns until it seats lightly. Make a note of this to use as a reference when reinstalling the pilot screws.

CAUTION

Remove the pilot screws and inspect them. Replace them if they are worn or damaged.

AIR CUT OFF VALVE

Remove the two screws, the set plate and the air cut off valve cover.

NOTE


Page 4-9


Visually check the following: Replace the air cut off valve as an assembly, if necessary.

CARBURETOR CLEANING

Separate the carburetors (page 4-12).
Remove the float valve, all jets, and the pilot screws.
Blow open all carburetor body openings with compressed air.

CARBURETOR ASSEMBLY


Page 4-10


INSTALLATION

If the air tube joint was removed, install a new O-ring onto the air tube joint.

Install the air cut off valve cover with the joint set plate and tighten the screws securely.
Be sure the diaphragm and spring are properly seated.

Install the pilot screws and return them to their original position as noted during removal.
Perform pilot screw adjustment if new pilot screws are installed (page 4-14).

NOTE


FLOAT CHAMBER, FLOAT AND JETS

Install the pilot screw and turn it in until it seats lightly.
Turn the pilot screw out the number of turns recorded during removal.

CAUTION

Install the valve seat, slow jet, needle jet and main jet.

Install the float with float valve in the carburetor body, then install the float arm pin through the body and the float.

Page 4-11


FLOAT LEVEL

Measure the float level with the float tang just contacting the float valve.

FLOAT LEVEL: 9.2 mm (0.36 in)

Adjust the float level by carefully bending the tang.

Install the new O-ring in the float chamber groove.

Install the float chamber and tighten the screws securely.

NOTE


 

VACUUM CHAMBER

Install the washer, jet needle, spring and jet needle holder in the vacuum piston.
Push the jet needle holder in and turn it in 90 degrees clockwise.

Hold the vacuum piston up to almost full open to avoid pinching the diaphragm with the chamber cover.

Page 4-12


Install the vacuum piston, aligning the tab of the diaphragm with the groove of the carburetor.

Install the chamber cover with the spring, aligning the cover with the hole in the carburetor, and secure with at least two screws before releasing the vacuum piston.

Install the fuel tubes as shown.

CARBURETOR
SEPARATION /ASSEMBLY

SEPARATION

Loosen the synchronization adjusting screw.

NOTE


Separate the carburetors by removing the two attaching screws.

Remove the synchronization spring.

Page 4-13


ASSEMBLY

I Loosen the synchronization adjusting screw until there is no spring tension.

Install the thrust spring between the throttle links.

Secure the carburetors together with the two screws.


  Install the synchronization spring and synchronization adjusting screw.

Inspect throttle operation as described below:


  Turn the throttle stop screw to align the rear cylinder carburetor
throttle valve with the edge of the bypass hole.

Align the front cylinder carburetor throttle valve with the bypass hole edge by turning the synchronization adjusting screw.

Make sure the throttle returns smoothly to the fully closed position.

Page 4-14


CARBURETOR INSTALLATION

Install the carburetors onto the cylinder heads and tighten the insulator bands securely.

Install the following parts:

Adjust as follows:

PILOT SCREW ADJUSTMENT

IDLE DROP PROCEDURE (U.S.A. ONLY)


NOTE

  1. Turn each pilot screw clockwise until it seats lightly and back it out to the specification given.
    This is an initial setting prior to the final pilot screw adjustment.

    INITIAL OPENING:
    49 St. modelCalifornia model
    '882-1/8 turns out2-1/2 turns out
    After
    '88
    Front: 1-1/2 turns out
    Rear: 1 turns out
    1-3/8 turns out
    CAUTION

  2. Warm up the engine to operating temperature.
    Stop and go riding for 10 minutes is sufficient.
  3. Attach a tachometer according to the manufacturer's instructions.
  4. Adjust the idle speed with the throttle stop screw.
  5. Turn each pilot screw 1/2 turn out from the initial setting.
  6. If the engine speed increases by 50 rpm or more, turn each pilot screw out by an additional 1/2 turn until engine speed drops by 50 rpm or less.
  7. Adjust the idle speed with the throttle stop screw.
  8. Turn the rear cylinder carburetor pilot screw in until the engine speed drops 50 rpm.
  9. Turn the rear cylinder carburetor pilot screw 1 turn out from the position obtained in step 8.
  10. Adjust the idle speed with the throttle stop screw.
  11. Perform steps 8, 9 and 10 for the front cylinder carburetor pilot screw.
  12. Drive new pilot screw plugs into the pilot screw bores with a 7 mm valve guide driver (P/N 07942 - 8230000). When fully seated the plug surfaces will be recessed 1 mm.

Page 4-15


HIGH ALTITUDE ADJUSTMENT
(U.S.A. only)

When the vehicle is to be operated continuously above 2,000m (6,500 feet) the carburetors must be readjusted as follows to improve driveability and decrease exhaust emissions.
Remove each pilot screw plug (page 4-7).
Warm up the engine to operating temperature. Stop and go riding for 10 minutes is sufficient.
Turn each pilot screw clockwise 1/2 turn.
Adjust the idle speed to specification with the throttle stop screw.


IDLE SPEED: 1,200 + 100 rpm

NOTE

Drive new pilot screw plugs into the pilot screw bores (page 4-7).
Attach a Vehicle Emission Control Information Update label on the left sub-frame upper pipe as shown. See SL#132 for information on obtaining the label.


NOTE

WARNING

When the vehicle is to be operated continuously below 1,500m (5,000 feet), turn each pilot screw counterclockwise 1/2 turn to its original position after removing each pilot screw plug and adjust the idle speed to specification (page 4-1). Drive new pilot screw plugs into the pilot screw bores (page 4-7). Be sure to do these adjustments at low altitude with the engine at normal operating temperature.

Page 4-16


PURGE CONTROL VALVE INSPECTION

(California model only)

NOTE

Check all fuel tank, Purge Control Valve (PCV), and charcoal canister hoses to be sure they are not kinked and are securely connected. Replace any hose that shows signs of damage or deterioration.


NOTE

Disconnect the PCV hoses from their connections and remove the PCV from its mount. Refer to the routing label on the air cleaner case cover for hose connections.

Connect a vacuum pump to the 8 mm (0.31 in.) I.D. hose No. 5 that goes to the 3-way joint. Apply the specified vacuum to the PCV.

SPECIFIED VACUUM: 250 mm (9.8 in) Hg

The specified vacuum should be maintained.
Replace the PCV if vacuum is not maintained.

TOOL:
Vacuum/Pressure pumpA937X-041-XXXXX or
Vacuum pumpST-AH-260-MC7 (U.S.A. only)

Remove the vacuum pump and connect it to the vacuum hose No. 11 that goes to the left carburetor body.
Apply the specified vacuum to the PCV.

SPECIFIED VACUUM: 250 mm (9.8 in) Hg

The specified vacuum should be maintained.
Replace the PCV if vacuum is not maintained.

TOOL:
Vacuum/Pressure pumpA937X-041-XXXXX or
Vacuum pumpST-AH-260-MC7 (U.S.A. only)

Connect a pressure pump to the 8 mm (0.31 in.) I.D. hose No. 4 that goes to the charcoal canister. While applying the specified vacuum to the PCV hose that goes to the 3-way joint pump air through the canister hose. Air should flow through the PCV and out of the hose that goes to the 3-way joint.
Replace the PCV if air does not flow out.

CAUTION

TOOL:
Vacuum/Pressure pumpA937X-041-XXXXX or
Vacuum pumpST-AH-260-MC7 (U.S.A. only)
Pressure pumpST-AH-255-MC7 (U.S.A. only)
Remove the pumps, install the PCV on its mount, route and reconnect the hoses according to the routing label (page 4-18).

Page 4-17


AIR VENT CONTROL VALVE INSPECTION

(California model only)

Disconnect the Air Vent Control Valve (AVCV) hoses from their connections and remove the AVCV from its mount. Refer to the routing label on the air cleaner case cover for hose connections.
Connect a vacuum pump to the No. 10 hose that goes to the right carburetor body.
Apply the specified vacuum to the AVCV.

SPECIFIED VACUUM: 250 mm (9.8 in) Hg

TOOL:
Vacuum/Pressure pumpA937X-041-XXXXX or
Vacuum pumpST-AH-260-MC7 (U.S.A. only)
The specified vacuum should be maintained. Replace the AVCV if vacuum is not maintained.

CAUTION

Connect the vacuum pump to the air vent port of the AVCV. Apply vacuum to the AVCV. The vacuum should hold steady. Replace the AVCV if vacuum leaks.
TOOL:
Vacuum/Pressure pumpA937X-041-XXXXX or
Vacuum pumpST-AH-260-MC7 (U.S.A. only)

Connect the vacuum pump to the No. 10 hose that goes to the right carburetor body.
Connect the pressure pump to the air vent port of the AVCV. While applying the vacuum to the AVCV No. 10 hose that goes to the right carburetor body, pump air through the air vent port.
Air should flow through the AVCV and out of the hose that goes to the carburetor air joint pipe.
TOOL:
Vacuum/Pressure pumpA937X-041-XXXXX or
Vacuum pumpST-AH-260-MC7 (U.S.A. only)
Pressure pumpST-AH-255-MC7 (U.S.A. only)

Plug the hose that goes to the carburetor air joint pipe.
While applying vacuum to the AVCV No. 10 hose that goes to the 3-way joint, apply air pressure. It should hold steady.

Replace the AVCV if pressure is not retained.
Remove the pumps, install the AVCV on its mount, route and reconnect the hoses according to the routing label.
TOOL:
Vacuum/Pressure pumpA937X-041-XXXXX or
Vacuum pumpST-AH-260-MC7 (U.S.A. only)
Pressure pumpST-AH-255-MC7 (U.S.A. only)

Page 4-18


SECONDARY AIR SUPPLY SYSTEM

(California model only)

SYSTEM INSPECTION

Start the engine and warm it up to normal operating temperature.
Disconnect the secondary air intake hose from the air cleaner case.

NOTE


Check that the secondary air intake ports are clean and free of carbon deposits.

Check the secondary air intake hose for clogging, deterioration or damage and replace if necessary.
Check the reed valves in the air suction valve (ASV) if the intake hose or supply hose is damaged by exhaust gas.
Disconnect the vacuum tube (No. 10) from the ASV and install a plug in the vacuum tube to keep air from entering.
Connect the vacuum pump to the ASV.
TOOL:
Vacuum/Pressure pumpA937X-041-XXXXX or
Vacuum pumpST-AH-260-MC7 (U.S.A. only)

Start the engine and open the throttle slightly to be certain that air is sucked in through the intake hose.
If air is not drawn in, check the air supply hoses and vacuum tube for clogging.
With the engine running, gradually apply vacuum to the ASV. Check that the air intake hose stops drawing air, and that the vacuum does not bleed off.

SPECIFIED VACUUM:
   300 - 370 mm (1 1.8 - 14.6 in) Hg

If air is still drawn in, or if the specified vacuum is not maintained, install a new ASV.
If afterburn occurs on deceleration, even when the secondary air supply system is normal, check the air cut-off valve for correct vacuum operation.

Page 4-19


REED VALVE INSPECTION

Disconnect the air supply hoses from the reed valve covers of the ASV.
Disconnect the vacuum tube and air intake hose from the ASV.
Remove the ASV mounting bolts and ASV.

Remove the two screws, the reed valve cover and the reed valve from the ASV.

Check the reed valve for damage or fatigue, and replace if necessary.

Install a new reed valve if the seat rubber is cracked or damaged, or if there is clearance between the reed valve and seat.

CAUTION

Assemble and install the ASV in the reverse order of disassembly/removal.

NOTE