4. FUEL SYSTEM

really big verson

SERVICE INFORMATION

• Gasoline is extremely flammable and is explosive under certain conditions. Work in a well ventilated area with the engine stopped.
  Do now smoke or allow flames or sparks in the work area or where gasoline is stored.
• If the engine must be running to do some work, make sure the area is well ventilated. Never run the engine in an enclosed area.
• The exhaust contains poisous carbon monoxide gas that may cause loss of conciousness and lead to death.

General

• Refer to section 3 for carburetor synchronization, throttle cable and choke cable adjustments.
• When disassembling fuel system parts, note the locations of the O-rings; Replace them with new ones on reassembly.
• The carburetor float chambers have drain screws that can be loosened to drain residual gasoline.
• For fuel pump inspection refer to section 18.
• All hoses used in the evaporative emission control system are numbered for identification. When connection one of these hoses, copare the hose number withthe Vacuum Hose Routing Diagram Lable on Page 4-15 (California model only), for its routing

• Do not bend or twist control cables. Camaged control cables will not operate smoothely and may stick or bind.

NOTE

• If the vehicle is to be stored for more than one month, drain the float chambers. Fuel left in the float chambers may cause clogged jets resulting in hard starting or poor driveability.

SPECIFICATIONS

TORQUE VALUES

TOOLS

TROUBLESHOOTING

Engine cranks but won't start

• No fuel to carburetor
• Engine flooded with fuel
• No spark at plug (ignition system faulty)
• clogged air cleaner
• Intake air leak
• Improper choke operation
• Improper throttle operation

Hard starting or stalling after starting

• Improper choke operation
• Ignition malfunction
• Faulty carburetor
• Fuel contaminated
• Intake air leak
• Incorrect idle speed
• Incorrect valve clearance (section 3)
• Incorrect carburetor syncronization (section 3)
• Improper choke valve operation

Rough idle

• Faulty ignition system
• Incorrect idle speed
• Incorrect valve clearance (section 3)
• Incorrect carburetor syncronization (section 3)
• Faulty carburetor
• Fuel contaminated
• Faulty air cut-off valve (California model only)
  • Faulty purge control valve
  • Faulty air vent control valve
  • worn/damaged emission system hoses

Afterburning during deceleration

• Faulty ignition system
• Faulty air cut-off valve (California model only)
• Lean mixture
  (California model only:)
  • worn/damaged emission system hoses

Misfiring during acceleration

• Faulty ignition system

Backfiring

• Faulty ignition system
• Faulty carburetor

Poor performance (drivability) and poor fuel economy

• Clogged fuel system
• Faulty ignition system
• Dirty air cleaner
• (California model only:)
  • Faulty air vent control valve
  • Worn/damaged emission system hoses

Lean mixture

• Clogged fuel jets
• Stuck vacuum piston
• Faulty float valve
• Low float level
• Clogged fuel tank breather
• Clogged fuel strainer
• Restricted fuel line
• Intake air leak
• Restricted or faulty fuel pump

Rich mixture

• Clogged air jets
• Faulty float valve
• Float level too high
• Dirty air cleaner

Page 4-3

FUEL TANK

REMOVAL

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

• If you remove the front mounting bolt first, it may damage the front mounting collar.

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

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

• The air cleaner case can be removed without removing the case cover removal.

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

• seat (page 13-25) and fuel tank (page 4-3)
• air cleaner case

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

• Gasoline is extremely flammable and is explosive under certain conditions. Work in a well ventilated area with the engine stopped. Do not smoke or allow flames or sparks in the work area or where gasoline is stored.

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

NOTE

• Turn the choke lever fully in to avoid losing the choke valves.

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

• The carburetors can be disassembled without being separated.

Remove the fuel tube from the carburetor.

VACUUM CHAMBER

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

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

• The pilot screws are factory pre-set and should not be removed unless the carburetors are overhauled.
• The pilot screw plugs are factory installed to prevent pilot screw misadjustment. Do not remove the plugs unless the pilot screws are being removed.
• Cover all openings with tape to keep metal particles out when the plugs are drilled.

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

• Be careful not to drill into the pilot screw.
• Both pilot screws must be replaced even if only one requires it, for proper pilot screw adjustment (page 4-14).

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

• Damage to the pilot screw seat will occur if the pilot screw is tightened against the seat.

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

AIR CUT OFF VALVE

NOTE

• The air cut off valve cover is under spring pressure. Do not loose the spring and screws.

Page 4-9

• diaphragm for deterioration, pin hole or other damage.
• spring for deterioration or other damage.
• diaphragm needle for excessive wear at the tip or other damage.
• orifice of air vent for clogging.
• O-ring for damage.

CARBURETOR CLEANING

CARBURETOR ASSEMBLY

INSTALLATION

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

• Do not install new plugs on new pilot screw holes until after adjustment has been made.
• If you replace the pilot screw in one carburetor, you must replace the pilot screw in the other carburetor for proper pilot screw adjustment.

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

• Damage to the pilot screw seat will occur if the pilot screw is tightened against the seat.

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

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

• Install the fuel tube clamps.

VACUUM CHAMBER

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

NOTE

• When separating the carburetors, be careful not to lose the thrust spring and synchronization adjusting spring.

Separate the carburetors by removing the two attaching screws.

Remove the synchronization spring.

Page 4-13

ASSEMBLY

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:

• Open the throttle slightly by rotating the throttle valve, then release the throttle. Make sure that there is no drag when opening and closing the throttle.

  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 following parts:

• air cleaner case
• fuel tank
• throttle cables
• choke cables

• pilot screw
• carburetor synchronization (page 3-8)
• throttle grip free play (page 3-4)
• carburetor idle speed (page 3-9)
• carburetor choke (page 3-5)

PILOT SCREW ADJUSTMENT

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

NOTE

• The pilot screws are factory pre-set and no adjustment is necessary unless the pilot screws are replaced.
• Use a tachometer with graduations of 50 rpm or smaller that will accurately indicate a 50 rpm change.

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. model	California model
   '88	2-1/8 turns out	2-1/2 turns out
   After '88	Front: 1-1/2 turns out Rear: 1 turns out	1-3/8 turns out

   CAUTION
   

   • Damage to the pilot screw seat will occur if the pilot screw is tightened against the seat.
   

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)

IDLE SPEED: 1,200 + 100 rpm

NOTE

• This adjustment must be made at high altitude to ensure proper high altitude operation.

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

• Do not attach the label to any part that can be easily removed from the vehicle.

WARNING

• Operation at an altitude lower than 1,500 m (S,OOO feet) with the carburetors adjusted for high altitudes may cause the engine to idle roughly and stall.

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)

• The purge control valve should be inspected if hot restart is difficult.

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

• The PCV is located under the fuel tank.

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 pump	A937X-041-XXXXX or
Vacuum pump	ST-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 pump	A937X-041-XXXXX or
Vacuum pump	ST-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

• To prevent damage to the purge control valve, do not use high pressure air sources. Use a hand operated air pump only.

TOOL:
Vacuum/Pressure pump	A937X-041-XXXXX or
Vacuum pump	ST-AH-260-MC7 (U.S.A. only)
Pressure pump	ST-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)

SPECIFIED VACUUM: 250 mm (9.8 in) Hg

TOOL:
Vacuum/Pressure pump	A937X-041-XXXXX or
Vacuum pump	ST-AH-260-MC7 (U.S.A. only)

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

CAUTION

• To prevent damage to the air vent control valve, do not use high pressure air sources. Use a hand operated air pump only.

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 pump	A937X-041-XXXXX or
Vacuum pump	ST-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 pump	A937X-041-XXXXX or
Vacuum pump	ST-AH-260-MC7 (U.S.A. only)
Pressure pump	ST-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 pump	A937X-041-XXXXX or
Vacuum pump	ST-AH-260-MC7 (U.S.A. only)
Pressure pump	ST-AH-255-MC7 (U.S.A. only)

Page 4-18

SECONDARY AIR SUPPLY SYSTEM

(California model only)

SYSTEM INSPECTION

NOTE

• Do not disconnect the fuel tubes from the tank.

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 pump	A937X-041-XXXXX or
Vacuum pump	ST-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

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

• Do not disassemble the reed valve assembly or bend the reed stopper.
• the stopper, reed or seat is faulty, replace the valve as an assembly.

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

NOTE

• After installing, make sure the air and vacuum tubes are correctly connected (page 1-10 to 15.).