sensor YAMAHA YZ250F 2008 Owners Manual

CONTENTS
CHAPTER 1
GENERAL INFOR-
MATION
DESCRIPTION ................. 1-1
MACHINE
IDENTIFICATION ............. 1-2
INCLUDED PARTS .......... 1-2
IMPORTANT
INFORMATION................. 1-2
CHECKING OF
CONNECTION .................. 1-3
SPECIAL TOOLS ............. 1-4
CONTROL FUNCTIONS .. 1-8
STARTING AND
BREAK-IN ........................ 1-8
TORQUE-CHECK
POINTS........................... 1-11
CLEANING AND
STORAGE ...................... 1-12
CHAPTER 2
SPECIFICATIONS
GENERAL
SPECIFICATIONS ............ 2-1
MAINTENANCE
SPECIFICATIONS ............ 2-3
TIGHTENING
TORQUES ...................... 2-10
LUBRICATION
DIAGRAMS .................... 2-16
CABLE ROUTING
DIAGRAM ....................... 2-18
CHAPTER 3
REGULAR INSPEC-
TION AND AD-JUSTMENTS
MAINTENANCE
INTERVALS ...................... 3-1
PRE-OPERATION
INSPECTION AND
MAINTENANCE................ 3-5
ENGINE ............................ 3-6
CHASSIS ........................ 3-14
ELECTRICAL ................. 3-23
CHAPTER 4 ENGINE
SEAT, FUEL TANK AND
SIDE COVERS.................. 4-1
EXHAUST PIPE AND
SILENCER ........................ 4-3
RADIATOR ....................... 4-5
CARBURETOR................. 4-7
CAMSHAFTS.................. 4-14
CYLINDER HEAD........... 4-19
VALVES AND VALVE
SPRINGS ........................ 4-21
CYLINDER AND
PISTON ........................... 4-25
CLUTCH ......................... 4-29
OIL FILTER ELEMENT
AND WATER PUMP ....... 4-34
BALANCER .................... 4-38
OIL PUMP ....................... 4-40
KICK SHAFT AND
SHIFT SHAFT ................. 4-44
CDI MAGNETO............... 4-49
ENGINE REMOVAL ....... 4-51
CRANKCASE AND
CRANKSHAFT ............... 4-55
TRANSMISSION, SHIFT
CAM AND SHIFT
FORK .............................. 4-61
CHAPTER 5CHASSIS
FRONT WHEEL AND
REAR WHEEL ..................5-1
FRONT BRAKE AND
REAR BRAKE ..................5-6
FRONT FORK ................. 5-16
HANDLEBAR..................5-24
STEERING ......................5-28
SWINGARM ....................5-32
REAR SHOCK
ABSORBER ....................5-37
CHAPTER 6
ELECTRICAL
ELECTRICAL
COMPONENTS AND
WIRING DIAGRAM ...........6-1
IGNITION SYSTEM...........6-2
THROTTLE POSITION
SENSOR SYSTEM ...........6-5
CHAPTER 7
TUNING
ENGINE.............................7-1
CHASSIS ..........................7-6

2-18
CABLE ROUTING DIAGRAM
CABLE ROUTING DIAGRAM
1. Fuel tank breather hose
2. Radiator hose 1
3. Connector cover
4. Cylinder head breather hose
5. Radiator hose 4
6. Clutch cable
7. Throttle position sensor lead
8. Carburetor breather hose
9. Upper engine bracket10. Hot starter cable
11. Fuel hose
12. Carburetor overflow hose
A. Insert the end of the fuel tank
breather hose into the hole in
the steering stem.
B. Install the connector cover so that it does not come in between
the radiator hose 1 and radiator. C. Aligh the paint mark on the cylin-
der head breather hose with the
front end of the hose guide.
D. Pass the cylinder head breather hose on the outside of the radia-
tor hose 1 and then between the
radiator 4 and frame.
E. Pass the clutch cable through
the cable guide.

2-19
CABLE ROUTING DIAGRAM
F. Pass the clutch cable in front of the radiator mounting boss.
G. Pass the fuel hose between the hot starter cable and throttle po-
sition sensor lead.
H. Pass the carburetor breater hos- es so that they are not pinched
between the upper engine
bracket and carburetor.
I. Pass the carburetor breather
hoses and overflow hose so that
all there hoses do not contact
the rear shock absorber.

2-20
CABLE ROUTING DIAGRAM
1. Hot starter cable
2. Radiator hose 2
3. Clamp
4. Ignition coil lead
5. Throttle position sensor lead
6. Hump (frame)
7. Oil hose
8. Hose guide
9. Neutral switch lead
10. CDI magneto lead
11. Clutch cable12. Radiator breather hose
13. Engine stop switch lead
14. Sub-wire harness
15. CDI unit bracket
16. CDI unit
17. Throttle cable
18. Cylinder head breather hose
A. Fasten the hot starter cable,
throttle cables, throttle position
sensor lead and ignition coil
lead. B. Fasten the throttle position sen-
sor lead behind the hump of the
frame.
C. Fasten the neutral switch lead on the oil hose.
D. Pass the neutral switch lead on the inside of the oil hose.
E. Fasten the neutral switch lead,
CDI magneto lead and radiator
breather hose.

4-7
CARBURETOR
CARBURETOR
REMOVING THE CARBURETOROrder Part name Q'ty Remarks Seat and fuel tank Refer to "SEAT, FUEL TANK AND SIDE
COVERS" section.
Rear shock absorber Refer to "REAR SHOCK ABSORBER" sec-
tion in the CHAPTER 5.
1Clamp 1
2 Throttle position sensor lead coupler 1
3 Throttle cable cover 1
4 Throttle cable 2
5 Clamp (air filter joint) 1 Loosen the screw (air filter joint).
6 Clamp (carburetor joint) 1 Loosen the screws (carburetor joint).
7 Hot starter plunger 1
8 Carburetor assembly 1
9 Carburetor joint 1
4 Nm (0.4 m kg, 2.9 ft lb)
4 Nm (0.4 m kg, 2.9 ft lb)
2 Nm (0.2 m kg, 1.4 ft lb)
3 Nm (0.3 m kg, 2.2 ft lb)
3 Nm (0.3 m kg, 2.2 ft lb)
11 Nm (1.1 m kg, 8.0 ft lb)
10 Nm (1.0 m kg, 7.2 ft lb)

4-10
CARBURETOR
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.
REMOVING THE PILOT SCREW
1. Remove:• Pilot screw "1"
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.
CHECKING THE CARBURETOR
1. Inspect:• Carburetor bodyContamination
→Clean.
• Use a petroleum based solvent for
cleaning. Blow out all passages and
jets with compressed air.
• Never use a wire.
2. Inspect:
•Main jet "1"
• Pilot jet "2"
• Needle jet "3"
• Starter jet "4"
• Pilot air jet "5"
• Leak jet "6" Damage
→Replace.
Contamination
→Clean.
• Use a petroleum based solvent for cleaning. Blow out all passages and
jets with compressed air.
• Never use a wire.
CHECKING THE NEEDLE VALVE
1. Inspect: • Needle valve "1"
• Valve seat "2"Grooved wear "a"
→Replace.
Dust "b"
→Clean.
•Filter "c" Clogged
→Clean.
CHECKING THE THROTTLE
VALVE
1. Check: • Free movementStick
→Repair or replace.
Insert the throttle valve "1" into the
carburetor body, and check for free
movement.
CHECKING THE JET NEEDLE
1. Inspect:• Jet needle "1"Bends/wear
→Replace.
• Clip groove
Free play exists/wear
→Replace.
• Clip position MEASURING AND ADJUSTING
THE FLOAT HEIGHT
1. Measure:
• Float height "a"
Out of specification
→Adjust.
Measurement and adjustment
steps:
a. Hold the carburetor in an upside down position.
• Slowly tilt the carburetor in the op-posite direction, then take the mea-
surement when the needle valve
aligns with the float arm.
• If the carburetor is level, the weight
of the float will push in the needle
valve, resulting in an incorrect mea-
surement.
b. Measure the distance between the mating surface of the float
chamber and top of the float using
a vernier calipers.
The float arm should be resting on the
needle valve, but not compressing
the needle valve.
c. If the float height is not within specification, inspect the valve
seat and needle valve.
d. If either is worn, replace them
both.
e. If both are fine, adjust the float height by bending the float tab "b"
on the float.
Standard clip position:No.5 Groove
Float height:
8.0 mm (0.31 in)

4-11
CARBURETOR
f. Recheck the float height.
CHECKING THE FLOAT
1. Inspect:•Float "1"Damage
→Replace.
CHECKING THE STARTER
PLUNGER
1. Inspect: • Cold starter plunger "1"
• Hot starter plunger "2"
Wear/damage
→Replace.
CHECKING THE ACCELERATOR
PUMP
1. Inspect: • Diaphragm (accelerator pump)
"1"
• Spring (accelerator pump) "2"
• Accelerator pump cover "3"
• O-ring "4"
• Push rod "5" Tears (diaphragm)/damage
→
Replace.
Dirt
→Clean.
2. Inspect: • Throttle shaft "1"
• Spring "2"
• Lever 1 "3"
• Spring 1 "4"
• Lever 2 "5" • Spring 2 "6"
Dirt
→Clean.
ASSEMBLING THE CARBURETOR
1. Install: • Cold starter plunger "1"
2. Install: • Pilot air jet "1"
3. Install: • Spring 1 "1"
• Lever 1 "2"
To lever 2 "3".
Make sure the spring 1 fits on the
stopper "a" of the lever 2.
4. Install:• Spring 2 "1"To lever 2 "2". 5. Install:
• Push rod link lever assembly "1"
Make sure the stopper "a" of the
spring 2 fits into the recess "b" in the
carburetor.
6. Install:• Washer "1"
•Circlip "2"
7. Install: • Spring "1"To throttle shaft "2".
Install the bigger hook "a" of the
spring fits on the stopper "b" of the
throttle shaft pulley.
8. Install:
• Throttle shaft assembly "1"
• Washer (metal) "2"
• Washer (resin) "3"
• Valve lever "4"
• Apply the fluorochemical grease on the bearings.
• Fit the projection "a" on the throttle
shaft assembly into the slot "b" in
the throttle position sensor.
• Make sure the stopper "c" of the
spring fits into the recess in the car-
buretor.
• Turn the throttle shaft assembly left
while holding down the lever 1 "5"
and fit the throttle stop screw tip "d"
to the stopper "e" of the throttle
shaft assembly pulley.

4-13
CARBURETOR
18. Install:• Carburetor breather hose "1"
Install the carburetor breather hoses
to the carburetor so that the hoses do
not bend near where they are in-
stalled.
ADJUSTING THE ACCELERATOR
PUMP TIMING
Adjustment steps:
In order for the throttle valve height
"a" to achieve the specified value,
tuck under the throttle valve plate "1"
the rod "2" etc. with the same outer di-
ameter as the specified value.
a. Fully turn in the accelerator pump adjusting screw "3".
b. Check that the link lever "4" has free play "b" by pushing lightly on
it.
c. Gradually turn out the adjusting screw while moving the link lever
until it has no more free play.
INSTALLING THE CARBURETOR
1. Install:
• Carburetor joint "1" 2. Install:
• Carburetor "1"
Install the projection "a" between the
carburetor joint slots.
3. Install:• Hot starter plunger "1"
4. Tighten: • Bolt (carburetor joint) "1"
• Bolt (air filter joint) "2"
5. Install: • Throttle cable (pull) "1" • Throttle cable (return) "2"
6. Adjust: • Throttle grip free playRefer to "ADJUSTING THE
THROTTLE CABLE FREE PLAY"
section in the CHAPTER 3.
7. Install: • Throttle cable cover "1"
• Bolt (throttle cable cover) "2"
8. Install: • Throttle position sensor lead cou-
pler "1"
•Clamp "2" Refer to "CABLE ROUTING DIA-
GRAM" section in the CHAPTER
2.
Throttle valve height:
0.8 mm (0.031 in)
Carburetor joint: 10 Nm (1.0 m•kg, 7.2
ft•lb)
Hot starter plunger:2 Nm (0.2 m•kg, 1.4
ft•lb)
Bolt (carburetor joint): 3 Nm (0.3 m•kg, 2.2
ft•lb)
Bolt (air filter joint): 3 Nm (0.3 m•kg, 2.2
ft•lb)
Throttle cable (pull): 4 Nm (0.4 m•kg, 2.9
ft•lb)
Throttle cable (return):11 Nm (1.1 m•kg, 8.0
ft•lb)
Bolt (throttle cable cov-
er): 4 Nm (0.4 m•kg, 2.9
ft•lb)

6-1
ELECTRICAL COMPONENTS AND WIRING DIAGRAM
ELECTRICAL
ELECTRICAL
COMPONENTS AND
WIRING DIAGRAM
ELECTRICAL COMPONENTS
1. Engine stop switch
2. Throttle position sensor
3. Neutral switch4. CDI magneto
5. Ignition coil
6. Spark plug7. CDI unit
WIRING DIAGRAM
1. Engine stop switch
2. Throttle position sensor
3. Neutral switch
4. CDI magneto
5. Ignition coil
6. Spark plug
7. CDI unit COLOR CODE
BBlack
Br Brown
GGreen
LBlue
OOrange
PPink
RRed
Sb Sky blue
WWhiteYYellow
B/L Black/Blue
B/W Black/White
B/Y Black/Yellow
G/B Green/Black
L/W Blue/White
R/W Red/White
B/WB/W
B/L
B/Y
SbSb
G/B
LYLY
P
B
B
B
B
G
O
WR
P
GW
R
P
B
Br W
W
B/Y G Br
G
RR
OB
Sb Sb
Y
Y
W Y
W
GG B
P P
Br BrRR
O L
B
Sb Y
LL
B/L
B/W
B/W
G/B
B
B
B/L
L
Sb
B/L
G/B
G/B B/Y
B/Y
B/W O
B/W
BrBrP

6-5
THROTTLE POSITION SENSOR SYSTEM
THROTTLE POSITION SENSOR SYSTEM
INSPECTION STEPS
If the throttle position sensor will not operate, use the following inspection steps.
*marked: Refer to "IGNITION SYSTEM" section.
Use the following special tools in this inspection.
Check entire ignition system for connection. No good→Repair or replace.
OK
↓
Check throttle position sensor. (Throttle position
sensor coil) No good→Replace.
OK
↓
*Check CDI magneto. (Charging coil) No good→Replace.
OK
↓
Check CDI unit. (Throttle position sensor input
voltage) No good→Replace.
Pocket tester:
YU-3112-C/90890-03112