2001 YAMAHA WR 426F fuel

5. GASOLINE IS HIGHLY FLAMMABLE.
Always turn off the engine while refu-
eling. Take care to not spill any gaso-
line on the engine or exhaust system.
Never refuel in the vicinity of an open
flame, or while smoking.
6. GASOLINE CAN CAUSE INJURY.
If you should swallow some gasoline,
inhale excess gasoline vapors, or
allow any gasoline to get into your
eyes, contact a doctor immediately. If
any gasoline spills onto your skin or
clothing, immediately wash skin areas
with soap and water, and change your
clothes.
7. ONLY OPERATE THE MACHINE IN AN
AREA WITH ADEQUATE VENTILA-
TION.
Never start the engine or let it run for
any length of time in an enclosed area.
Exhaust fumes are poisonous. These
fumes contain carbon monoxide,
which by itself is odorless and color-
less. Carbon monoxide is a dangerous
gas which can cause unconscious-
ness or can be lethal.
8. PARK THE MACHINE CAREFULLY;
TURN OFF THE ENGINE.
Always turn off the engine if you are
going to leave the machine. Do not
park the machine on a slope or soft
ground as it may fall over.
9. THE ENGINE EXHAUST PIPE, MUF-
FLER, AND OIL TANK WILL BE VERY
HOT AFTER THE ENGINE HAS BEEN
RUN.
Be careful not to touch them or to
allow any clothing item to contact
them during inspection or repair.
10. PROPERLY SECURE THE MACHINE
BEFORE TRANSPORTING IT.
When transporting the machine in
another vehicle, always be sure it is
properly secured and in an upright
position and that the fuel cock is in
the “OFF” position. Otherwise, fuel
may leak out of the carburetor or fuel
tank.

EC050000
TO THE NEW OWNER
This manual will provide you with a good basic
understanding of features, operation, and
basic maintenance and inspection items of this
machine. Please read this manual carefully
and completely before operating your new
machine. If you have any questions regarding
the operation or maintenance of your machine,
please consult your Yamaha dealer.
NOTE:

This manual should be considered a perma-
nent part of this machine and should remain
with it even if the machine is subsequently
sold.
EC060000
NOTICE
Some data in this manual may become out-
dated due to improvements made to this
model in the future. If there is any question
you have regarding this manual or your
machine, please consult your Yamaha
dealer.
EC070001
Weights of machines without fuel
The minimum weights for motocross
machines are:
for the class 125 cc....................... minimum
88 kg (194 lb)
for the class 250 cc....................... minimum
98 kg (216 lb)
for the class 500 cc....................... minimum
102 kg (225 lb)
In modifying your machine (e.g., for weight
reduction), take note of the above limits of
weight.
F.I.M. MACHINE WEIGHTS:

EC0A0000
CONTENTS
CHAPTER 1
GENERAL INFORMATION
DESCRIPTION
.......................................... 1-1
MACHINE IDENTIFICATION
.................... 1-2
IMPORTANT INFORMATION
................... 1-3
CHECKING OF CONNECTION
................ 1-6
SPECIAL TOOLS
...................................... 1-7
CONTROL FUNCTIONS
......................... 1-10
FUEL
....................................................... 1-13
STARTING AND BREAK-IN
................... 1-14
TORQUE-CHECK POINTS
..................... 1-18
CLEANING AND STORAGE
.................. 1-19
CHAPTER 2
SPECIFICATIONS
GENERAL SPECIFICATIONS
(WR426F)
.................................................. 2-1
MAINTENANCE SPECIFICATIONS
(WR426F)
.................................................. 2-4
GENERAL SPECIFICATIONS
(WR400F)
................................................ 2-18
MAINTENANCE SPECIFICATIONS
(WR400F)
................................................ 2-21
GENERAL TORQUE
SPECIFICATIONS
.................................. 2-35
DEFINITION OF UNITS
.......................... 2-35
LUBRICATION DIAGRAMS
................... 2-36
CABLE ROUTING DIAGRAM
................ 2-38

CHAPTER 3
REGULAR INSPECTION AND
ADJUSTMENTS
MAINTENANCE INTERVALS
................... 3-1
PRE-OPERATION INSPECTION
AND MAINTENANCE
............................... 3-4
ENGINE
..................................................... 3-5
CHASSIS
................................................. 3-26
ELECTRICAL
.......................................... 3-47
CHAPTER 4
ENGINE
SEAT, FUEL TANK
AND SIDE COVERS
................................. 4-1
EXHAUST PIPE AND SILENCER
............ 4-2
RADIATOR
................................................ 4-4
CARBURETOR
......................................... 4-8
CAMSHAFTS
.......................................... 4-21
CYLINDER HEAD
................................... 4-28
VALVES AND VALVE SPRINGS
........... 4-32
CYLINDER AND PISTON
....................... 4-41
CLUTCH (WR426F)
................................ 4-48
CLUTCH (WR400F)
................................ 4-55
OIL FILTER, WATER PUMP
AND CRANKCASE COVER (RIGHT)
.... 4-62
BALANCER
............................................ 4-69
OIL PUMP
............................................... 4-72
KICK AXLE AND SHIFT SHAFT
............ 4-76
CDI MAGNETO
....................................... 4-83
ENGINE REMOVAL
................................ 4-87
CRANKCASE AND CRANKSHAFT
....... 4-92
TRANSMISSION, SHIFT CAM
AND SHIFT FORK
................................ 4-101

1 - 1
GEN
INFO

DESCRIPTION
EC100000
GENERAL INFORMATION
EC110000
DESCRIPTION
1
Clutch lever
2
Decompression lever
3
“ENGINE STOP” button
4
Trip meter
5
Lights switch
6
Front brake lever
7
Throttle grip
8
Radiator cap
9
Fuel tank cap
0
Oil filler plug/dipstick
A
Tail light
B
Kick starter
C
Fuel tank
D
Headlight
E
Radiator
F
Coolant drain bolt
G
Rear brake pedal
H
Valve joint
I
Fuel cock
J
Cold starter knob
K
Hot starter knob (red)
L
Air cleaner
M
Drive chain
N
Shift pedal
O
Front fork
NOTE:

l
The machine you have purchased may differ
slightly from those shown in the following.
l
Designs and specifications are subject to
change without notice.
1
1

1 - 12
GEN
INFO
CONTROL FUNCTIONS
FUEL COCK
The fuel cock supplies fuel from the tank to
carburetor and also filters the fuel. The fuel
cock has three positions:
OFF:With the lever in this position fuel will not
flow. Always return the lever to this posi-
tion when the engine is not running.
ON: With the lever in this position fuel flows to
the carburetor. Normal riding is done with
the lever in this position.
RES:With the lever in this position fuel flows to
the carburetor from the reserve section of
the fuel tank after the main supply of the
fuel has been depleted. Normal riding is
possible with the lever is in this position,
but it is recommended to add fuel as
soon as possible.
COLD STARTER KNOB
When cold, the engine requires a richer air-fuel
mixture for starting. A separate starter circuit,
which is controlled by the cold starter knob 1,
supplies this mixture. Pull the cold starter knob
out to open the circuit for starting. When the
engine has warmed up, push it in to close the
circuit.
HOT STARTER KNOB (red)
The hot starter knob (red) 1 is used when
starting a warm engine.
Use the hot starter knob when starting the
engine again immediately after it was stopped
(the engine is still warm). Pulling out the hot
starter knob injects secondary air to thin the
air-fuel mixture temporarily, allowing the
engine to be started more easily.
CAUTION:
After the engine has started, be sure to
push the hot starter knob back in.

1 - 13
GEN
INFO
CONTROL FUNCTIONS/FUEL
EC15F000
VALVE JOINT
This valve joint 1 prevents fuel from flowing
out and is installed to the fuel tank breather
hose.
CAUTION:
In this installation, make sure the arrow
faces the fuel tank and also downward.
LIGHTS SWITCH
The lights switch 1 is located on the handle-
bar.
FLAP
In order to prevent water from entering the car-
buretor while the motorcycle is operated in the
rain, attach the accessory flap 1 to the frame
at the rear of the fuel tank.
NOTE:
Riding with the flap attached when it is not
raining can help keep out dust, dirt and sand.
FUEL
Always use the recommended fuel as stated
below. Also, be sure to use new gasoline the
day of a race.
NOTE:
Except for AUS:
1. If knocking or pinging occurs, use a dif-
ferent brand of gasoline or higher octane
grade.
2. If unleaded gasoline is not available, then
leaded gasoline can be used.
Recommended fuel:
Except for AUS:
Premium unleaded fuel with a
research octane number of 95
or higher.
For AUS:
Unleaded fuel only

1 - 14
GEN
INFO
STARTING AND BREAK-IN
STARTING AND BREAK-IN
WARNING
Never start or run the engine in a closed
area. The exhaust fumes are poisonous;
they can cause loss of consciousness and
death in a very short time. Always operate
the machine in a well-ventilated area.
CAUTION:
lThe carburetor on this motorcycle has a
built-in accelerator pump. Therefore,
when starting the engine, do not operate
the throttle or the spark plug will foul.
lUnlike a two-stroke engine, this engine
cannot be kick started when the throttle is
open because the kick starter may kick
back. Also, if the throttle is open the air/
fuel mixture may be too lean for the
engine to start.
lNever use the decompression lever after
the engine is started. The engine may be
damaged if you use the decompression
lever while it is running.
lBefore starting the machine, perform the
checks in the pre-operation check list.
STARTING A COLD ENGINE
1. Inspect the coolant level.
2. Turn the fuel cock to “ON”.
3. Shift the transmission into neutral.
4. Fully open the cold starter knob.
5. Without pulling in the decompression
lever, slowly depress the kick starter until
the compression stroke is found. When
considerable resistance of the kick starter
is felt, the engine is on the compression
stroke. If the engine is on the exhaust
stroke, resistance will only be felt when
the kick starter is initially depressed, not
through the entire range of depression
(as when the engine is on the compres-
sion stroke); therefore, depress the kick
starter a few more times.