Haynes Yamaha Xv V Twins Manual

							
3A-16

Chapter 3 Part A Fuel and exhaust systems (XV535 models)

9.1 Loosen the throttle cable adjuster

locknuts and loosen the adjusters

(arrows) 
9.2 Remove the screw that secures the

throttle cables to the housing 
9.3a Slip the cable out of its groove .

9.3b ... and disengage the end from

the pulley 
9.4a Pull the end of the cable out of the

socket and slip the cable sideways

through the slot to disengage it... 
9.4b ... then slide the end of the cable

sideways out of the pulley

9 Throttle cables and grip - removal, installation and

adjustment

Refer to illustrations 9.1, 9.2, 9.3a, 9.3b, 9.4a and 9.4b

Removal

1 Loosen the throttle cabfe(s) with the adjusters (see illustration).

2 Remove the throttle cable securing screw at the handlebar (see

illustration).

3 Remove the handlebar switch mounting screws.. Separate the

halves of the handlebar switch and detach the throttle cable(s) from the

throttle grip pulley (see illustrations).

4 Detach the throttle cables from the throttle pulley at the

carburetors (see illustrations). Remove the cables, noting how they

are routed.

5 Slide the throttle grip off the handlebar.

Installation

6 Clean the handlebar and apply a light coat of multi-purpose

grease.

7 Route the cable(s) into place, following the same route as noted n

removal - the cables should pass behind the upper part of the right

fork leg. Make sure they dont interfere with any other components and

arent kinked or bent sharply.

8 Lubricate the ends of the accelerator cable (and decelerator cable 
if equipped) with multi-purpose grease and connect them to the

throttle pulleys at the carburetors and at the throttle grip.

Adjustment

9 Follow the procedure outlined in Chapter 1, Throttle

operation/grip freeplay - check and adjustment, to adjust the cables.

10 Turn the handlebars back and forth to make sure the cables dont

cause the steering to bind. With the engine idling, turn the handlebars

back and forth and make sure idle speed doesnt change. If it does,

find and fix the cause before riding the motorcycle.

10 Exhaust system - removal and installation

Removal

Refer to illustrations 10.2a, 10.2b, 10.3a, 10.3b, 10.4, 10.5 and 10.6

1 Support the bike securely so it cant be knocked over during this

procedure.

2 Remove the nuts that secure the front exhaust pipe to the cylinder

head (see illustrations).

3 Remove the Allen bolts and detach the rear exhaust pipe from the

joint pipe at the cylinder head (see illustration). Remove the nuts and

detach the joint pipe from the head (see illustration).

4 Unbolt the muffler/silencer bracket at the right passenger footpeg

(see illustration). 
						

							
Chapter 3 Part A Fuel and exhaust systems (XV535 models)

3A-17

10.2a Exhaust system (XV535 models) - exploded view

1 Exhaust pipe gaskets

2 Exhaust pipe-to-rear

joint gasket 
3 Joint pipe (rear cylinder)

4 Exhaust pipe assembly 
5 Support the muffler/silencer chamber with a jack and unbolt it

from the frame (see illustration). Lower the exhaust system away from

the bike and take it out.

6 Installation is the reverse of removal, with the following additions:

a) Use new gaskets at the cylinder head (see illustration).

b) Tighten all fasteners to the torque settings listed in this Chapters

Specifications.

11 Fuel pump - circuit check and fuel pump test

1 With the engine kill switch in the On position, the fuel pump

should start and run for approximately five seconds after the ignition is

switched on (with the fuel warning light on or off). It should shut off

once the carburetor float chambers are full, then run again once the

engine is started.

2 The fuel pump circuit consists of the pump, the pump relay, the

igniter unit (which controls the fuel pump as well as ignition timing), the

engine kill switch, the ignition switch, the main and ignition fuses, the

battery and related wiring.

3 Lift the seat and prop it up.

4 Check the battery condition and charge (see Chapter 1 and

Chapter 8).

5 Check the main and ignition fuses, the ignition switch and the

engine kill switch (see Chapter 8). Replace them if theyre defective,

then try the fuel pump again.

10.2b Detach the front exhaust pipe

flange from the cylinder head 
10.3a Remove the Allen bolts and

disconnect the rear exhaust pipe from

the joint... 
10.3b ... and remove the nuts that

secure the rear joint to the cylinder head

10.4 Unbolt the bracket at the right

passenger footpeg 
10.5 With the exhaust system supported,

unbolt the muffler/silencer chamber 
10.6 Use new gaskets for installation 
						

							
3A-18

Chapter 3 Part A Fuel and exhaust systems (XV535 models)

11.6 Connect the positive lead (1) of a

0-20 volt voltmeter to the red/white wire

terminal of the connector (2) and the

negative lead to ground/earth (3) 
11.10 Connect a short jumper wire (arrow)

between the red/white and blue/black

wire terminals 
11.11 Connect the voltmeter positive (1)

lead to the back of the blue-black wire

terminal (2) and the negative lead to

ground/earth (3)

11.13 Connect the voltmeter positive lead (1) to the red/green

wire terminal in the harness side of the connector (2) and the

negative lead to ground/earth (3)

Pump wont run, fuel warning light off

Refer to illustrations 11.6, 11.10 and 11.11

6 If the pump wont run while the engine is running, or if it wont run

for five seconds with the ignition switch On, the kill switch in Run and

the fuel warning light off, check battery voltage to the pump.

Disconnect the electrical connector at the relay and connect a 0-20

volt DC voltmeter between the red/white wire terminal in the harness

and a good grounding/earthing point (bare metal on the engine) (see

illustration).

7 Turn the ignition switch to On and the engine kill switch to Run,

then push the Start switch. The voltmeter should indicate at least 12

volts.

8 If the reading is less than 12 volts, check the wiring in the fuel

pump circuit for breaks or bad connections. Be sure to check the

battery terminal connections and the battery ground/earth cable

connection to the motorcycle.

9 If the reading is at least 12 volts, the wiring is good. Check the

fuel reserve switch (see Chapter 8).

a) If the reserve switch is bad, replace it

b) If the pump wont run with the engine running, go to Step 10. If

the pump wont run for five seconds with the ignition switch On

and the kill switch in Run, go to Step 11.

10 Disconnect the electrical connector from the fuel pump relay (see

illustration). Connect a short length of wire between the blue/black

wire terminal and the red/white wire terminal in the harness side of the 
relay connector. With the ignition switch On and the kill switch in Run,

push the Start and Reserve switches. The fuel pump should run.

a) If the fuel pump wont run, test it (see below).

b) If the fuel pump now runs, check the wiring and connections in

the fuel pump circuit. If theyre good, the fuel pump relay is

probably defective. Replace it.

11 Reconnect the connector to the fuel pump relay. Insert the

voltmeter positive probe into the back of the blue/black wire connector

and connect the voltmeter negative lead to ground/earth (bare metal

on the motorcycle) (seeIllustration). With the ignition switch On and

the kill switch in Run, push the Start and Reserve switches. The

voltmeter should indicate at least 11 volts.

a) If voltage is less than 11 volts, the fuel pump relay is probably

defective. Replace it.

b) If voltage is 11 volts or more, check the wiring and connections in

the fuel pump circuit. If theyre good, the fuel pump is probably

defective. Test it (see below).

Pump wont run, fuel warning light on

Refer to illustration 11.13

12 If the pump wont run for five seconds with the ignition switch On,

the kill switch in Run and the fuel warning light on, check the fuel

reserve switch (see Chapter 8).

a) If the fuel reserve switch is bad, replace it.

b) If the switch is good, go to Step 13.

13 Disconnect the electrical connector from the fuel pump relay (see

illustration). Connect the positive lead of a 0-20 volt voltmeter to the

red-green wire in the harness side of the connector and the negative

voltmeter lead to a good grounding/earthing point (bare metal on the

engine). With the ignition switch On and the engine kill switch in Run,

push the start switch.

a) If its less than 12 volts, check the wiring and connections in the

fuel pump circuit.

b) If its 12 volts or more, perform Step 11 above.

Pump wont shut off after 30 seconds

Refer to illustrations 11.14

14 Disconnect the fuel sender electrical connector (see illustration).

Connect the terminals in the harness side of the sender connector to

each other with a short length of wire.

15 With the sender harness terminals connected to each other,

connect the positive lead of a 0-20 volt voltmeter to the back side of

the blue/black wire terminal in the fuel pump relay connector (see

illustration 11.11). Connect the voltmeter negative lead to a good

grounding/earthing point (bare metal on the engine).

16 With the ignition switch On and the kill switch in Run, push the 
						

							
Chapter 3 Part A Fuel and exhaust systems (XV535 models) 
3A-19

11.14 Connect the terminals in the

harness side of the fuel sender connector

to each other with a short jumper wire 
12.2 Disconnect the wiring connector and

remove the fuel pump relay 
12.5 Loosen the fuel line clamps (A),

disconnect the connector (B), remove the

mounting bolts (C) and take the pump out;

loosen the clamp screw (D) to remove the

pump from its bracket

Start switch and note the voltmeter reading.

a) If the reading is zero after about 30 seconds, the fuel sender is

probably defective. Test it as described in Chapter 8.

b) If the reading is more than zero after about 30 seconds, check the

wiring and connections in the fuel pump circuit. If theyre good,

the fuel pump relay is probably defective. Replace it.

Fuel pump test

17 Disconnect the wiring connector from the fuel pump. Connect the

pump directly to the battery with two lengths of wire (positive to

blue/black; negative to black). If the pump doesnt run, replace it.

12 Fuel pump and relay - replacement

Fuel pump relay replacement

Refer to illustration 12.2

1 Remove the right front side cover (see Chapter 7).

2 Disconnect the wiring connector from the relay (see illustration).

3 Remove the relay from its mounting bracket, install a new one and

reconnect the wiring connector.

Fuel pump replacement

Refer to illustration 12.5

4 Remove the left rear side cover (see Chapter 7).

5 Loosen the fuel line clamps and push the ends of the fuel lines off

the pump fittings (see illustration).

6 Disconnect the pump electrical connector. Remove the mounting

bolts and take the pump out (see illustration 12.5).

7 Loosen the clamp screw and slide the pump out of its bracket.

8 Installation is the reverse of the removal steps.

13 Air induction system (1990-on US models) - inspection

and component replacement

Refer to illustrations 13.1, 13.3a, 13.3b and 13.3c

1 The air induction system uses exhaust gas pulses to suck fresh

air into the exhaust ports, where it mixes with hot combustion gases.

The additional oxygen provided by the fresh air allows combustion to

continue for a longer time, reducing unburned hydrocarbons in the

exhaust (see illustration). Reed valves allow the flow of air into the

ports and prevent exhaust gas from flowing into the system. The air cut

valve shuts off the flow of air into the system during deceleration to

prevent backfiring. 
13.1 Air induction

system details

1 Reed valve

2 Air cleaner

3 Air cut valve

4 Rear cylinder

carburetor joint

A To cylinders

B To air cut valve

C To no. 1 cylinder

D To no. 2 cylinder 
						

							
3A-20

Chapter 3 Part A Fuel ahd exhaust systems (XV535 models)

13.3a Pipe connections at the cylinder

heads are secured by screw-type

hose clamps 
13.3b The pipes are attached to the

right side of the engine with two Allen

bolts (arrows) 
13.3c Hose-to-pipe connections are

secured by spring-type clamps

2 Check the hoses for loose connections, damage and deterio-

ration. Tighten or replace loose or damaged hoses.

3 To replace system components, remove the left side cover (see

Chapter 7). Disconnect the air hoses and the metal tubes (see

illustrations), remove the mounting screws and take the assembly off

the motorcycle (see illustrations).

4 Installation is the reverse of the removal steps.

14 Evaporation control system (California models) -

inspection and canister replacement

Refer to illustration 14.1

1 The evaporation control system used on California models

prevents fuel vapor from escaping into the atmosphere. When the

engine isnt running, the vapor is stored in a canister, then routed into

the combustion chambers for burning when the engine starts (see

illustration).

2 The hoses should be checked periodically for loose connections,

damage and deterioration. Tighten or replace the hoses as needed.

3 To remove the canister, disconnect the hoses and remove the

mounting bolts. To install it, bolt the canister to the motorcycle and

reconnect the hoses.

Rollover valve

4 The rollover valve allows passage of vapors to the canister when

its in its normal upright position. The valve is designed to block the

flow of vapors if the motorcycle is rolled over.

5 To test the valve, disconnect its hoses and remove the mounting

screw (see illustration 14.1). It should be possible to blow air through

the valve when its upright, but not when its turned upside down. If the

valve doesnt perform as described, replace 
14.1 Evaporation control system details (California models)

1 To carburetor 3 Canister

2 Fuel tank 
						

							
3B-1

Chapter 3 Part B

Fuel and exhaust systems (XV700-1100 models)

Contents

Section

Air filter element - servicing See Chapter 1

Air induction system (XV1000, XV1100 and 1988

and laterXV750) - inspection and component replacement.... 15

Carburetor overhaul - general information 5

Carburetors and intake joints - removal and installation 6

Carburetors - disassembly, inspection, cleaning and reassembly 7

Carburetors - fuel level adjustment 8

Choke cable - removal and installation 10

Evaporation control system (California models) - inspection

and canister replacement 16

Exhaust system - removal and installation 11

Fuel pump - circuit check and fuel pump test 12 
Section

Fuel pump - replacement 13

Fuel system - check and filter replacement See Chapter 1

Fuel tank - cleaning and repair ... 3

Fuel tank - removal and installation 2

General information 1

Idle fuel/air mixture adjustment - general information 4

Idle speed - check and adjustment See Chapter 1

Mixture control valve (all 1981 through 1983 models;

1984 and 1985 XV700) - testing and replacement 14

Throttle cables and grip - removal, installation and adjustment.... 9

Throttle operation/grip freeplay - check and adjustment See Chapter 1

Specifications

XV700 models

Fuel tank capacity

Total 12.5 liters (3.3 US gal, 2.7 Imperial gal)

Reserve 2.5 liters (0.6 US gal, 0.5 Imperial gal)

Carburetors

Type Hitachi HSC40 (two)

Main jet

Rear cylinder 128

Front cylinder . 132

Main air jet 50

Jet needle Y-32

Needle jet 3.2

Pilot air jet . 190

Pilot jet 42

Pilot screw Preset (turns out not specified)

Valve seat size... 2.0

Starter jet 40

Fuel level: 0+/-1.0 mm (0+/- 0.039 inch)

Tightening torques

Carburetor joint bolts 10 Nm (7.2 ft-lbs)

Exhaust pipe-to-cylinder head nuts 20 Nm (14 ft-lbs)

XV750 models (1981 through 1983)

Fuel tank capacity

Total . . 12 liters (3.17 US gal, 2.64 Imperial gal)

Reserve . 2.6 liters (0.67 US gal, 0.57 Imperial gal) 
						

							
3B-2 
Chapter 3 Part B Fuel and exhaust systems (XV700-1100 models)

Carburetors

Type Hitachi HSC40 (two)

Main jet 122

Main air jet 50

Jet needle (US models)

Rear cylinder . Y-23

Front cylinder .... Y-22

Jet needle (UK models)

Rear cylinder Y-21

Front cylinder Y-20

Needle jet Not specified

Pilot air jet

US . 185

UK 180

Pilot jet . 41

Pilot screw Preset (turns out not specified)

Valve seat size 2.0

Starter jet 40

Fuel level

Rear cylinder 1.0 +/- 1.0 mm (0.039 +/-0.039 inch)

Front cylinder 2.0 +/-1.0 mm (0.078 +/- 0.039 inch)

Tightening torques

Carburetor joint bolts . 10 Nm (7.2 ft-lbs)

Exhaust pipe-to-cylinder head nuts 20 Nm (14 ft-lbs)

XV750 models (1988-on)

Fuel tank capacity

Total 14.5 liters (3.8 US gal, 3.2 Imperial gal)

Reserve 2.5 liters (0.65 US gal, 0.5 Imperial gal)

Carburetors

Type . Mikuni BST40 (two)

Main jet 122.5

Main air jet . 80

Jet needle 5DL12

Needle jet . . Y-4

Pilot air jet 60

Pilot jet 40

Pilot screw . Preset (turns out not specified)

Valve seat size 2.3

Starter jet 35

Fuel level 1.5 to 2.5 mm (0.6 to 1.0 inch)

Tightening torques

Carburetor joint bolts 10 Nm (7.2 ft-lbs)

Exhaust pipe-to-cylinder head nuts 20 Nm (14 ft-lbs)

XV920 shaft drive models

Fuel tank capacity

Total 14.5 liters (3.83 US gal, 3.19 Imperial gal)

Reserve 2.0 liters (0.53 US gal, 0.44 Imperial gal)

Carburetors

Type Hitachi HSC40 (two)

Main jet

Rear cylinder 126

Front cylinder . 128

Main air jet 50

Jet needle

Rear cylinder Y-25

Front cylinder Y-24

Needle jet . Not specified

Pilot air jet

US 185

UK 180

Pilot jet. . 41

Pilot screw Preset (turns out not specified)

Valve seat size 2.0

Starter jet . ....... ... 40 
						

							
Chapter 3 Part B Fuel and exhaust systems (XV700-1100 models)

3B-3

Fuel level

Rear cylinder 1.0 +/-1.0 mm (0.039 +/- 0.039 inch)

Front cylinder :.. 2.0 +/-1.0 mm (0.078 +/- 0.039 inch)

Tightening torques

Carburetor joint bolts 10 Nm (7.2 ft-lbs)

Exhaust pipe-to-cylinder head nuts 20 Nm (14 ft-lbs)

XV920 chain drive models

Fuel tank capacity

Total ... 19 liters (5.02 US gal, 4.18 Imperial gal)

Reserve .... 3.2 liters (0.84 US gal, 0.70 Imperial gal)

Carburetors

Type Hitachi HSC40 (two)

Main jet

Rear cylinder 126

Front cylinder 124

Main air jet 50

Jet needle

Rear cylinder . Y-22

Front cylinder Y-22

Needle jet . Not specified

Pilot air jet 18

Pilot jet . 41

Pilot screw . Preset (turns out not specified)

Valve Seat size 2.0

Starter jet 40

Fuel level

Rear cylinder.. . 1.0 +/-1.0 mm (0.039 +/- 0.039 inch)

Front cylinder 2.0 +/-1.0 mm (0.078 +/- 0.039 inch)

Tightening torques

Carburetor joint bolts 10 Nm (7.2 ft-lbs)

Exhaust pipe-to-cylinder head nuts 20 Nm (14 ft-lbs)

XV1000 shaft drive models

Fuel tank capacity

Total... 14.5 liters (3.8 US gal, 3.2 Imperial gal)

Reserve ... 3.0 liters (0.79 US gal, 0.66 Imperial gal)

Carburetors

Type ... Hitachi HSC40 (two)

Main jet

Rear cylinder . . 124

Front cylinder . 132

Main air jet . ... 50

Jet needle

Rear cylinder Y-34

Front cylinder Y-33

Needle jet . .. 3.2

Pilot air jet . 190

Pilot jet 40

Pilot screw Preset (turns out not specified)

Valve seat size 2.0

Starter jet 40

Fuel level 0 +/-1.0 mm (0 +/- 0.039 inch)

Tightening torques

Carburetor joint bolts 10 Nm (7.2 ft-lbs)

Exhaust pipe-tojsylinder head nuts . 20 Nm (14 ft-lbs)

XV1000 chain drive models (TR1)

Fuel tank capacity

Total 19 liters (5.02 US gal, 4.18 Imperial gal)

Reserve 3.8 liters (1.0 US gal, 0.84 Imperial gal)

Carburetors

Type Hitachi HSC40 (two) 
						

							
3B-4 
Chapter 3 Part B Fuel and exhaust systems (XV700-1100 models)

Main jet .

Rear cylinder 126

Front cylinder 124

Main air jet 50

Jet needle

Rear cylinder Y-21

Front cylinder Y-20

Needle jet . Not specified

Pilot air jet 175

Pilot jet 43

Pilot screw .... Preset (turns out not specified)

Valve seat size 2.0

Starter jet . 40

Fuel level

Rear cylinder 1.0 +/-1.0 mm (0.039 +/- 0.039 inch)

Front cylinder 2.0 +/-1.0 mm (0.078 +/- 0.039 inch)

Tightening torques

Carburetor joint bolts 10 Nm (7.2 ft-lbs)

Exhaust pipe-to-cylinder head nuts 20 Nm (14 ft-lbs)

XV1100 models (1986 and 1987)

Fuel tank capacity

Total . 16.8 liters (4.43 US gal, 3.69 Imperial gal)

Reserve 3.0 liters (0.79 US gal, 0.66 Imperial gal)

Carburetors

Type Hitachi HSC40 (two)

Main jet

Rear cylinder 122

Front cylinder 128

Main air jet 50

Jet needle Y-33

Needle jet 3.2

Pilot air jet 100

Pilot jet 40

Pilot screw Preset (turns out not specified)

Valve seat size.. 1.4

Starter jet.... 40

Fuel level 0 +/-1.0 mm (0 +/- 0.039 inch)

Tightening torques

Carburetor joint bolts 10 Nm (7.2 ft-lbs)

Exhaust pipe-to-cylinder head nuts 20 Nm (14 ft-lbs)

XV1100 models (1988-on)

Fuel tank capacity

Total 16.8 liters (4.43 US gal, 3.69 Imperial gal)

Reserve 3.0 liters (0.79 US gal, 0.66 Imperial gal)

Carburetors

Type Mikuni BST40 (two)

Main jet

Rear cylinder 122.5

Front cylinder 125

Main air jet 80

Jet needle 5DL8

Needle jet Y-4

Pilot air jet

No. 1 60

No. 2 140

Pilot jet 40

Pilot screw Preset (turns out not specified)

Valve seat size 1.5

Starter jet 35

Fuel level 1.5 to 2.5 mm (0.6 to 1.0 inch)

Tightening torques

Carburetor joint bolts 10 Nm (7.2 ft-lbs)

Exhaust pipe-to-cylinder head nuts 20 Nm (14 ft-lbs) 
						

							
Chapter 3 Part B Fuel and exhaust systems (XV700-1100 models)

3B-5

1 General information

The fuel system consists of the fuel tank, the fuel tap and filter,

the carburetors and the connecting lines, hoses and control cables.

XV1000 and XV1100 models use an electric fuel pump.

The carburetors used on these motorcycles are two Hitachis

(1981 through 1987) or Mikunis (1988 and later) with butterfly-type

throttle valves. For cold starting, an enrichment circuit is actuated by a

choke lever mounted on the left side of the bike.

The exhaust system routes exhaust gases into a pair of mufflers

(silencers) which are mounted on either side of the bike or both on the

right side, depending on model.

Many of the fuel system service procedures are considered routine

maintenance items and for that reason are included in Chapter 1.

2 Fuel tank - removal and installation

Warning: Gasoline (petrol) is extremely flammable, so take extra

precautions when you work on any part of the fuel system. Dont smoke

or allow open flames or bare light bulbs near the work area, and dont

work in a garage where a natural gas-type appliance (such as a water

heater or clothes dryer) is present. If you spill any fuel on your skin,

rinse it off immediately with soap and water. When you perform any

kind of work on the fuel system, wear safety glasses and have a fire

extinguisher suitable for class B fires (flammable liquids) on hand.

Refer to illustration 2.3

1 Support the bike securely so it cant be knocked over during this

procedure.

2 Remove the seat (see Chapter 7).

3 Detach the rear end of the tank from the motorcycle. If youre

working on an early model, remove the clip (see illustration). If youre

working on a later model, remove the bolt.

4 Pull the tank backward to separate it from its mounting dampers.

Label and disconnect the hoses and wires and remove the tank from

the motorcycle.

5 Before installing the tank, check the condition of the hoses

and rubber mounting dampers - if theyre hardened, cracked, or show

any other signs of deterioration, replace them.

6 To install the tank, reverse the above procedure. Make sure the

tank seats properly and does not pinch any control cables or wires.

3 Fuel tank - cleaning and repair

1 All repairs to the fuel tank should be carried out by a professional

who has experience in this critical and potentially dangerous work.

Even after cleaning and flushing of the fuel system, explosive fumes

can remain and ignite during repair of the tank.

2 If the fuel tank is removed from the vehicle, it should not be

placed in an area where sparks or open flames could ignite the fumes

coming out of the tank. Be especially careful inside garages where a

natural gas-type appliance is located, because the pilot light could

cause an explosion.

4 Idle fuel/air mixture adjustment - general information

1 Due to the increased emphasis on controlling motorcycle exhBust

emissions, certain governmental regulations have been formulated

which directly affect the carburetion of this machine. In order to

comply with the regulations, the carburetors on some models have a

metal sealing plug pressed into the hole over the pilot screw (which

controls the idle fuel/air mixture) on each carburetor, so they cant be

tampered with. These should only be removed in the event of a

complete carburetor overhaul, and even then the screws should be

returned to their original settings. The pilot screws on other models are

accessible, but the use of an exhaust gas analyzer is the only accurate 
2.3 On early models, remove the clip (shown) to detach the rear

end of the tank; on later models, remove the mounting bolt

way to adjust the idle fuel/air mixture and be sure the machine doesnt

exceed the emissions regulations.

2 If the engine runs extremely rough or blows black smoke at idle or

continually stalls, and if a carburetor overhaul does not cure the

problem, take the motorcycle to a Yamaha dealer service department

or other repair shop equipped with an exhaust gas analyzer. They will

be able to properly adjust the idle fuel/air mixture to achieve a smooth

idle and restore low speed performance.

5 Carburetor overhaul - general information

1 Poor engine performance, hesitation, hard starting, stalling,

flooding and backfiring are all signs that major carburetor maintenance

may be required.

2 Keep in mind that many so-called carburetor problems are really

not carburetor problems at all, but mechanical problems within the

engine or ignition system malfunctions. Try to establish for certain that

the carburetors are in need of maintenance before beginning a major

overhaul.

3 Check the fuel filter, the fuel lines, the fuel tank breather hose(s),

the rollover valve (if equipped), the intake manifold hose clamps, the

vacuum hoses, the air filter element, the cylinder compression, the

spark plugs, the carburetor synchronization and the fuel pump before

assuming that a carburetor overhaul is required.

4 Most carburetor problems are caused by dirt particles, varnish

and other deposits which build up in and block the fuel and air

passages. Also, in time, gaskets and O-rings shrink or deteriorate and

cause fuel and air leaks which lead to poor performance.

5 When the carburetor is overhauled, it is generally disassembled

completely and the parts are cleaned thoroughly with a carburetor

cleaning solvent and dried with filtered, unlubricated compressed air.

The fuel and air passages are also blown through with compressed air

to force out any dirt that may have been loosened but not removed by

the solvent. Once the cleaning process is complete, the carburetor is

reassembled using new gaskets, O-rings and, generally, a new inlet

needle valve and seat.

6 Before disassembling the carburetors, make sure you have a

carburetor rebuild kit (which will include all necessary O-rings and

other parts), some carburetor cleaner, a supply of rags, some means of

blowing out the carburetor passages and a clean place to work. It is

recommended that only one carburetor be overhauled at a time to

avoid mixing up parts.

7 • Dont separate the carburetors from each other unless one of the

joints between them is leaking. The carburetors can be overhauled

completely without being separated, and reconnecting them properly

can be difficult.