2008 YAMAHA YZ250F change time

FOREWARD
INTRODUCTION
Congratulations on your purchase of
a Yamaha YZ series. This model is
the culmination of Yamaha's vast ex-
perience in the production of paceset-
ting racing machines. It represents
the highest grade of craftsmanship
and reliability that have made Yama-
ha a leader.
This manual explains operation, in-
spection, basic maintenance and tun-
ing of your machine. If you have any
questions about this manual or your
machine, please contact your Yama-
ha dealer.
Yamaha continually seeks advance-
ments in product design and quality.
Therefore, while this manual contains
the most current product information
available at the time of printing, there
may be minor discrepancies between
your machine and this manual. If you
have any questions concerning this
manual, please consult your Yamaha
dealer.
PLEASE READ THIS MANUAL
CAREFULLY AND COMPLETELY
BEFORE OPERATING THIS MA-
CHINE. DO NOT ATTEMPT TO OP-
ERATE THIS MACHINE UNTIL YOU
HAVE ATTAINED A SATISFACTO-
RY KNOWLEDGE OF ITS CON-
TROLS AND OPERATING
FEATURES AND UNTIL YOU HAVE
BEEN TRAINED IN SAFE AND
PROPER RIDING TECHNIQUES.
REGULAR INSPECTIONS AND
CAREFUL MAINTENANCE,
ALONG WITH GOOD RIDING
SKILLS, WILL ENSURE THAT YOU
SAFETY ENJOY THE CAPABILI-
TIES AND THE RELIABILITY OF
THIS MACHINE.
PARTICULARLY IMPORTANT
INFORMATION
The Safety Alert Symbol means AT-
TENTION! BECOME ALERT! YOUR
SAFETY IS INVOLVED!
Failure to follow WARNING instruc-
tions could result in severe injury or
death to the machine operator, a by-
stander, or a person inspecting or re-
pairing the machine. A CAUTION indicates special pre-
cautions that must be taken to avoid
damage to the machine.
A NOTE provides key information to
make procedures easier or clearer.
IMPORTANT NOTICE
THIS MACHINE IS DESIGNED
STRICTLY FOR COMPETITION
USE, ONLY ON A CLOSED
COURSE. It is illegal for this machine
to be operated on any public street,
road, or highway. Off-road use on
public lands may be illegal. Please
check local regulations before riding.
1. THIS MACHINE IS TO BE OP-
ERATED BY AN EXPERI-
ENCED RIDER ONLY.
Do not attempt to operate this
machine at maximum power
until you are totally familiar
with its characteristics.
2. THIS MACHINE IS DESIGNED TO BE RIDDEN BY THE OP-
ERATOR ONLY.
Do not carry passengers on
this machine.
3. ALWAYS WEAR PROTEC- TIVE APPAREL.
When operating this ma-
chine, always wear an ap-
proved helmet with goggles
or a face shield. Also wear
heavy boots, gloves, and pro-
tective clothing. Always wear
proper fitting clothing that
will not be caught in any of
the moving parts or controls
of the machine.
4. ALWAYS MAINTAIN YOUR MACHINE IN PROPER
WORKING ORDER.
For safety and reliability, the
machine must be properly
maintained. Always perform
the pre-operation checks in-
dicated in this manual. Cor-
recting a mechanical problem
before you ride may prevent
an accident.
5. GASOLINE IS HIGHLY FLAM-MABLE.
Always turn off the engine
while refueling. Take care to
not spill any gasoline on the
engine or exhaust system.
Never refuel in the vicinity of
an open flame, or while
smoking.
6. GASOLINE CAN CAUSE IN- JURY.
If you should swallow some
gasoline, inhale excess gaso-
line vapors, or allow any gas-
oline to get into your eyes,
contact a doctor immediately.
If any gasoline spills onto
your skin or clothing, imme-
diately wash skin areas with
soap and water, and change
your clothes.
7. ONLY OPERATE THE MA- CHINE IN AN AREA WITH AD-
EQUATE VENTILATION.
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 mon-
oxide, which by itself is odor-
less and colorless. Carbon
monoxide is a dangerous gas
which can cause uncon-
sciousness or can be lethal.
8. PARK THE MACHINE CARE- FULLY; TURN OFF THE EN-
GINE.
Always turn off the engine if
you are going to leave the
machine. Do not park the ma-
chine on a slope or soft
ground as it may fall over.
9. THE ENGINE, EXHAUST PIPE, MUFFLER, 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 in-
spection or repair.

7-6
CHASSIS
CHASSIS
SELECTION OF THE SECONDARY
REDUCTION RATIO (SPROCKET)
ondary gear reduction ratio>
• It is generally said that the second-ary gear ratio should be reduced for
a longer straight portion of a speed
course and should be increased for
a course with many corners. Actual-
ly, however, as the speed depends
on the ground condition of the day
of the race, be sure to run through
the circuit to set the machine suit-
able for the entire course.
• In actuality, it is very difficult to achieve settings suitable for the en-
tire course and some settings may
be sacrificed. Thus, the settings
should be matched to the portion of
the course that has the greatest ef-
fect on the race result. In such a
case, run through the entire course
while making notes of lap times to
find the best balance; then, deter-
mine the secondary reduction ratio.
• If a course has a long straight por-
tion where a machine can run at
maximum speed, the machine is
generally set such that it can devel-
op its maximum revolutions toward
the end of the straight line, with care
taken to avoid the engine over-rev-
ving.
Riding technique varies from rider to
rider and the performance of a ma-
chine also vary from machine to ma-
chine. Therefore, do not imitate other
rider's settings from the beginning but
choose your own setting according to
the level of your riding technique.
DRIVE AND REAR WHEEL
SPROCKETS SETTING PARTS
TIRE PRESSURE
Tire pressure should be adjust to suit
the road surface condition of the cir-
cuit.
• Under a rainy, muddy, sandy, or slippery condition, the tire pressure
should be lower for a larger area of
contact with the road surface.
• Under a stony or hard road condi- tion, the tire pressure should be
higher to prevent a flat tire.
FRONT FORK SETTING
The front fork setting should be made
depending on the rider's feeling of an
actual run and the circuit conditions. The front fork setting includes the fol-
lowing three factors:
1. Setting of air spring characteris-
tics
• Change the fork oil amount.
2. Setting of spring preload • Change the spring.
3. Setting of damping force • Change the compression damp-ing.
• Change the rebound damping. The spring acts on the load and
the damping force acts on the
cushion travel speed.
CHANGE IN AMOUNT AND
CHARACTERISTICS OF FORK OIL
Damping characteristic near the final
stroke can be changed by changing
the fork oil amount.
Adjust the oil amount in 5 cm3 (0.2
Imp oz, 0.2 US oz) increments or
decrements. Too small oil amount
causes the front fork to produce a
noise at full rebound or the rider to
feel some pressure on his hands
or body. Alternatively, too large oil
amount will cause the air spring
characteristics to have a tendency
to be stiffer with the consequent
deteriorated performance and
characteristics. Therefore, adjust
the front fork within the specified
range.
A. Air spring characteristics in relation to oil amount change
B. Load
Secondary reduction ratio =
Number of rear wheel sprocket
teeth/Number of drive sprocket
teeth
Standard secondary
reduction ratio 49/13
(3.769)
Part name Size Part number
Drive
sprocket "1" (STD) 13T 9383B-13218
Rear wheel
sprocket "2" 47T 1C3-25447-00
48T 1C3-25448-00
(STD) 49T 1C3-25449-00 50T 1C3-25450-00
51T 1C3-25451-00
52T 1C3-25452-00
Standard tire pressure: 100 kPa (1.0 kgf/cm
2,
15 psi)
Extent of adjustment: 60–80 kPa (0.6–0.8 kgf/
cm
2, 9.0–12 psi)
Extent of adjustment: 100–120 kPa (1.0–1.2
kgf/cm
2, 15–18 psi)
Standard oil amount:330 cm3 (11.6 Imp oz,
11.2 US oz)
Extent of adjustment: 300–375 cm
3(10.6–13.2
Imp oz, 10.1–12.7 US
oz)