fuel YAMAHA WR 426F 2001 Owner's Guide

4 - 11
ENGCARBURETOR
EC466020
HANDLING NOTE
CAUTION:
Do not loosen the screws {TPS (throttle
position sensor)} 1 except when changing
the TPS (throttle position sensor) due to
failure because it will cause a drop in
engine performance.
REMOVAL POINTS
Pilot screw
1. Remove:
lPilot screw 1
NOTE:
To optimize the fuel flow at a small throttle
opening, each machine’s pilot screw has been
individually set at the factory. Before removing
the pilot screw, turn it in fully and count the
number of turns. Record this number as the
factory-set number of turns out.
INSPECTION
Carburetor
1. Inspect:
lCarburetor body
Contamination ® Clean.
NOTE:
lUse a petroleum based solvent for cleaning.
Blow out all passages and jets with com-
pressed air.
lNever use a wire.

ENG
4 - 21
CAMSHAFTS
CAMSHAFTS
CYLINDER HEAD COVER
Extent of removal:1 Cylinder head cover removal
Extent of removal Order Part name Q’ty Remarks
CYLINDER HEAD COVER
REMOVAL
Preparation for removal Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Carburetor Refer to “CARBURETOR” section.
1 Spark plug 1
2 Engine upper bracket (right) 1
3 Engine upper bracket (left) 1
4 Cylinder head breather hose 1
5 Oil tank breather hose 1
6 Bolt (cylinder head cover) 2
7 Cylinder head cover 1
8 Gasket 1
9 Timing chain guide (upper) 1
1

ENG
4 - 28
CYLINDER HEAD
CYLINDER HEAD
CYLINDER HEAD
Extent of removal:1 Cylinder head removal
Extent of removal Order Part name Q’ty Remarks
CYLINDER HEAD REMOVAL
Preparation for removal Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Exhaust pipe and silencer Refer to “EXHAUST PIPE AND
SILENCER” section.
Radiator Refer to “RADIATOR” section.
Carburetor Refer to “CARBURETOR” section.
Camshaft Refer to “CAMSHAFTS” section.
1 Decompression cable 1
2 Cable guide 1
3 Bolt 1
4 Decompression shaft 1
5 Oil delivery pipe 1
6 Nut (M6) 2
7 Nut (M8) 2
8 Bolt (L = 150 mm) 2
9 Bolt (L = 160 mm) 2
10 Cylinder head 1
1

ENG
4 - 83
CDI MAGNETO
EC4L0000
CDI MAGNETO
Extent of removal:1 CDI magneto removal
Extent of removal Order Part name Q’ty Remarks
CDI MAGNETO REMOVAL
Preparation for removal Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Bolt [radiator (left)]
Disconnect the CDI magneto
lead.Refer to “RADIATOR” section.
1 Engine guard (left) 1
2 Shift pedal 1
3 Crankcase cover (left) 1
4 Gasket 1
5 Dowel pin 2
6 Nut (rotor) 1 Use special tool.
Refer to “REMOVAL POINTS”.
7 Rotor 1
8 Stator 1
9Woodruff key
1
1

ENG
4 - 87
ENGINE REMOVAL
EC4M0000
ENGINE REMOVAL
Extent of removal Order Part name Q’ty Remarks
ENGINE REMOVAL
Preparation for removal Hold the machine by placing the
suitable stand under the frame.
WARNING
Support the machine securely so there is nodanger of it falling over.
Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Carburetor Refer to “CARBURETOR” section.
Exhaust pipe and silencer Refer to “EXHAUST PIPE AND
SILENCER” section.
Clutch cable Disconnect at engine side.
Decompression cable and guide Disconnect at engine side.
Radiator Refer to “RADIATOR” section.
Shift pedal Refer to “CDI MAGNETO” section.
Cylinder head breather hose and
oil tank breather hoseRefer to “CAMSHAFTS” section.
Drain the engine oil Refer to “ENGINE OIL REPLACEMENT”
section in the CHAPTER 3.
Spark plug cap
Disconnect the CDI magneto lead.

5 - 45
CHASHANDLEBAR
NOTE:
lThe “ENGINE STOP” button, clutch lever
holder, decompression lever holder and
clamp should be installed according to the
dimensions shown.
lPass the “ENGINE STOP” button lead in the
middle of the clutch holder.
9. Install:
lClutch cable 1
lDecompression cable 2
NOTE:
Apply the lithium soap base grease on the
clutch cable end and decompression cable
end.
10. Adjust:
lClutch lever free play
Refer to “CLUTCH ADJUSTMENT”
section in the CHAPTER 3.
lDecompression lever free play
Refer to “DECOMPRESSION LEVER
ADJUSTMENT” section in the CHAP-
TER 3.
B
2
1
11. Insert the end of the fuel breather hose
1 into the hole of the steering shaft.

5 - 59
CHASREAR SHOCK ABSORBER
EC580000
REAR SHOCK ABSORBER
Extent of removal:1 Rear shock absorber removal2 Rear shock absorber disassembly
Extent of removal Order Part name Q’ty Remarks
Preparation for removalREAR SHOCK ABSORBER
REMOVAL
Hold the machine by placing the
suitable stand under the engine.
WARNING
Support the machine securely so there is nodanger of it falling over.
Seat, fitting band and side covers Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section in the CHAPTER 4.
Silencer Refer to “EXHAUST PIPE AND
SILENCER” section in the CHAPTER 4.
Drain the coolant. Refer to “COOLANT REPLACEMENT”
section in the CHAPTER 3.
Coolant reservoir tank Refer to “RADIATOR” section in the
CHAPTER 4.
1 Tail light connector 2
2 Band 2
3 Bolt (reservoir tank) 1
4 Clamp (air cleaner joint) 1 Only loosening.
5 Rear frame 1
6 Bolt (rear shock absorber-relay arm) 1Hold the swingarm.
7 Bolt (rear shock absorber-frame) 1
8 Rear shock absorber 1
12

6 - 3
–+ELEC

IGNITION SYSTEM
EC620000
IGNITION SYSTEM
INSPECTION STEPS
Use the following steps for checking the possibility of the malfunctioning engine being attributable to
ignition system failure and for checking the spark plug which will not spark.
*: Only when the ignition checker is used.
NOTE:

l
Remove the following parts before inspection.
1) Seat
2) Fuel tank
l
Use the following special tools in this inspection.
Spark gap test*Clean or replace
spark plug.
Check entire ignition
system for connection.Repair or replace.
Check “ENGINE STOP”
button.Replace.
Check ignition coil. Primary coil Replace.
Secondary coilReplace.
Check CDI magneto. Pick-up coil Replace.
Source coil Replace.
Check neutral switch. Repair or replace.
Replace CDI unit.
Dynamic spark tester:
YM-34487
Ignition checker:
90890-06754
Pocket tester:
YU-3112-C/90890-03112
No Spark
OK
OK
OK
OK
Spark
No good
No good
No good
No good
No good
No good
No good
OK

6 - 7
–+ELECTPS (THROTTLE POSITION SENSOR) SYSTEM
EC69000
TPS (THROTTLE POSITION SENSOR) SYSTEM
INSPECTION STEPS
If the TPS will not operate, use the following inspection steps.
*marked: Refer to “IGNITION SYSTEM” section.
NOTE:
lRemove the following parts before inspection.
1) Seat
2) Fuel tank
lUse the following special tools in this inspection.
Check entire ignition
system for connection.Repair or replace.
Check TPS. TPS coil Replace.
*Check CDI magneto. Source coil Replace.
Check CDI unit.TPS input
voltageReplace.
Pocket tester:
YU-3112-C/90890-03112Inductive tachometer:
YU-08036-B
Engine tachometer:
90890-03113
No good
No good
No good
No good
OK
OK
OK

6 - 11
–+ELECLIGHTING SYSTEM
LIGHTING SYSTEM
INSPECTION STEPS
Refer to the following flow chart when inspecting the ignition system for possible ploblems.
NOTE:
lReplace the bulb and/or bulb socket.
1) Seat
2) Fuel tank
lUse the following special tool.
Check the bulb and bulb
socket.Replace the bulb and/
or bulb socket.
Check the lights switch. Replace.
Check the CDI magneto. Lighting coil Replace.
Check the entire lighting sys-
tem proper for connections.Repair or replace.
Replace the regulator.
Pocket tester:
YU-3112-C/90890-03112
OK
OK
OK
OK
No good
No good
Improperly connected
No good