2009 YAMAHA YZ250F engine oil

6-7
THROTTLE POSITION SENSOR SYSTEM
HANDLING NOTE
Do not loosen the screw (throttle
position sensor) "1" except when
changing the throttle position sen-
sor due to failure because it will
cause a drop in engine perfor-
mance.
CHECKING THE COUPLERS AND
LEADS CONNECTION
1. Check:
• Couplers and leads connection
Rust/dust/looseness/short-circuit
→Repair or replace.
CHECKING THE THROTTLE
POSITION SENSOR COIL
1. Inspect:
• Throttle position sensor coil resis-
tance
Out of specification→Replace.
2. Loosen:
• Throttle stop screw "1"
Turn out the throttle stop screw until
the throttle shaft is in the full close po-
sition.
3. Inspect:
• Throttle position sensor coil vari-
able resistance
Check that the resistance in in-
creased as the throttle grip is
moved from the full close position
to the full open position.
Out of specification→Replace.
CHANGING AND ADJUSTING THE
THROTTLE POSITION SENSOR
1. Remove:
• Throttle position sensor coupler
•Carburetor
2. Remove:
• Screw (throttle position sensor)
"1"
• Throttle position sensor "2"
Loosen the screw (throttle position
sensor) using the T25 bit.
3. Replace:
• Throttle position sensor
4. Install:
• Throttle position sensor "1"
• Screw (throttle position sensor)
"2"
• Align the slot "a" in the throttle posi-
tion sensor with the projection "b"
on the carburetor.
• Temporarily tighten the screw
(throttle position sensor).
5. Install:
•Carburetor
• Throttle position sensor coupler
6. Adjust:
• Engine idling speed
Refer to "ADJUSTING THE EN-
GINE IDLING SPEED" section in
the CHAPTER 3.
7. Insert the thin electric conductors
"2" (lead) into the throttle position
sensor coupler "1", as shown, and
connect the tester to them.
• Do not insert the electric conduc-
tors more than required because
it may reduce the waterproof
function of the coupler.
• Make sure that a short-circuit
does not develop between the
terminals because it may cause
damage to electrical compo-
nents.
8. Start the engine.
9. Adjust:
• Throttle position sensor output
voltage
Adjustment steps:
a. Adjust the installation angle of the
throttle position sensor "1" to ob-
tain the specified output voltage. Tester (+) lead→Blue lead "1"
Tester (-) lead→Black lead "2"
Throttle po-
sition sen-
sor coil
resistanceTester se-
lector posi-
tion
4–6 kΩ at
20°C (68 °F) kΩ×1
Tester (+) lead→Yellow lead "1"
Tester (-) lead→Black lead "2"
Throttle position
sensor coil vari-
able resistanceTester
selec-
tor po-
sition
Full
closedFull
opened
kΩ×1 Zero –3
kΩat
20°C
(68 °F)4–6
kΩat
20 °C
(68 °F)
Tester (+) lead→Yellow lead "3"
Tester (-) lead→Black lead "4"

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.
Secondary reduction ratio =
Number of rear wheel sprocket
teeth/Number of drive sprocket
teeth
Standard secondary
reduction ratio49/13
(3.769)
* 51/13
(3.923)
* Except for USA and CDN
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
* (STD) 51T 1C3-25451-00
52T 1C3-25452-00
* Except for USA and CDN
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)

7-7
CHASSIS
A. Air spring characteristics in
relation to oil amount change
B. Load
C. Stroke
1. Max. oil amount
2. Standard oil amount
3. Min. oil amount
SETTING OF SPRING AFTER
REPLACEMENT
As the front fork setting can be easily
affected by rear suspension, take
care so that the machine front and
rear are balanced (in position, etc.)
when setting the front fork.
1. Use of soft spring
• Change the rebound damping.
Turn out one or two clicks.
• Change the compression damp-
ing.
Turn in one or two clicks.
Generally a soft spring gives a soft
riding feeling. Rebound damping
tends to become stronger and the
front fork may sink deeply over a se-
ries of gaps.
2. Use of stiff spring
• Change the rebound damping.
Turn in one or two clicks.
• Change the compression damp-
ing.
Turn out one or two clicks.
Generally a stiff spring gives a stiff
riding feeling. Rebound damping
tends to become weaker, resulting in
lack of a sense of contact with the
road surface or in a vibrating handle-
bar.
FRONT FORK SETTING PARTS
• Front fork spring "1"
The I.D. mark (slits) "a" is proved on
the end of the spring.
REAR SUSPENSION SETTING
The rear suspension setting should
be made depending on the rider's
feeling of an actual run and the circuit
conditions.
The rear suspension setting includes
the following two factors:
1. Setting of spring preload
• Change the set length of the
spring.
• Change the spring.
2. Setting of damping force
• Change the rebound damping.
• Change the compression damp-
ing.CHOOSING SET LENGTH
1. Place a stand or block under the
engine to put the rear wheel
above the floor, and measure the
length "a" between the rear wheel
axle center and the rear fender
holding bolt.
2. Remove the stand or block from
the engine and with a rider astride
the seat, measure the sunken
length "b" between the rear wheel
axle center and the rear fender
holding bolt.
3. Loosen the locknut "1" and make
adjustment by turning the spring
adjuster "2" to achieve the stan-
dard figure from the subtraction of
the length "b" from the length "a".
• If the machine is new and after it is
broken in, the same set length of
the spring may change because of
the initial fatigue, etc. of the spring.
Therefore, be sure to make reeval-
uation.
• If the standard figure cannot be
achieved by adjusting the spring
adjuster and changing the spring
set length, replace the spring with
an optional one and make readjust-
ment.
TY
PESPRIN
G
RATESPRING PART
NUMBERI.D.
MA
RK
(slit
s)
SO
FT0.398 1C3-23141-A1 |
0.408 1C3-23141-B1 ||
0.418 1C3-23141-C1 |||
0.428 1C3-23141-D1 ||||
0.438 1C3-23141-E1 |||||
ST
D0.449 5XC-23141-N0 —
*ST
D0.459 1C3-23141-G1 |-||
STI
FF0.469 1C3-23141-H1 |-|||
0.479 1C3-23141-J1 |-||||
* Except for USA and CDN
Standard figure:
90–100 mm (3.5–3.9 in)