2008 YAMAHA WR 250F air filter

3-11
ENGINE
2. Adjust:• Throttle grip free play
Throttle grip free play adjustment
steps:
a. Slide the adjuster cover.
b. Loosen the locknut "1".
c. Turn the adjuster "2" until the
specified free play is obtained.
d. Tighten the locknut.
Before adjusting the throttle cable
free play, the engine idle speed
should be adjusted.
After adjusting the throttle cable
free play, start the engine and turn
the handlebar to right and left and
make sure that the engine idling
does not run faster.
LUBRICATING THE THROTTLE
1. Remove: • Cover (throttle cable cap) "1"
• Cover (grip cap) "2"
• Throttle grip cap "3"
2. Apply: • Lithium soap base grease
On the throttle cable end "a". 3. Install:
• Throttle grip cap
• Screw (throttle grip cap)
• Cover (grip cap)
• Cover (throttle cable cap)
ADJUSTING THE HOT STARTER
LEVER FREE PLAY
1. Check: • Hot starter lever free play "a"Out of specification →Adjust.
2. Adjust: • Hot starter lever free play
Hot starter lever free play adjust-
ment steps:
a. Loosen the locknut "1".
b. Turn the adjuster "2" until free
play "a" is within the specified lim-
its.
c. Tighten the locknut.
After adjustment, check proper oper-
ation of hot starter.
CLEANING THE AIR FILTER
ELEMENT
Proper air filter maintenance is the
biggest key to preventing premature
engine wear and damage.
Never run the engine without the
air filter element in place; this
would allow dirt and dust to enter
the engine and cause rapid wear
and possible engine damage.
1. Open the air filter case cover "1"
Loosen the quick screw "2" and pull
on it to open the air filter case cover.
2. Unhook: •Binder "1"
3. Remove: • Air filter element "1"
• Air filter guide "2"
4. Clean: • Air filter element
Clean them with solvent.
After cleaning, remo ve the remaining
solvent by squeezing the element.
• Do not twist the element when squeezing the element.
• Leaving too much of solvent in
the element may result in poor
starting.
Locknut: 4 Nm (0.4 m•kg, 2.9
ft•lb)
Screw (throttle grip cap):4 Nm (0.4 m•kg, 2.9
ft•lb)
Hot starter lever free play
"a": 3–6 mm (0.12–0.24 in)
Locknut: 4 Nm (0.4 m•kg, 2.9
ft•lb)

3-12
ENGINE
5. Inspect:• Air filter elementDamage →Replace.
6. Apply:
• Foam-air-filter oil or equivalent oil to the element
• Squeeze out the excess oil. Ele-ment should be wet but not drip-
ping.
• Wipe off the oil left on the element surface using a clean dry cloth. (Ex-
cess oil in the element may ad-
versely affect engine starting.)
7. Install:• Air filter guide "1"
• Align the projection "a" on filter guide with the hole "b" in air filter el-
ement.
• Apply the lithium soap base grease on the matching surface "c" on air
filter element.
8. Install:
• Air filter element "1"
Align the projection "a" on filter guide
with the hole "b" in air filter case.
9. Hook:•Binder "1"
Hook the binder "1" so that it contacts
the filter guide projections "a".
CHECKING THE ENGINE OIL
LEVEL
1. Start the engine, warm it up for several minutes, and then turn off
the engine and wait for five min-
utes.
2. Place the machine on a level
place and hold it up on upright po-
sition by placing the suitable
stand under the engine.
3. Inspect: • Oil levelOil should be up to the full level in
the check window "1".
Level check window is not full. →
Add 0.2 L (0.18 Imp qt, 0.21 US
qt) of oil.
(For USA and CDN)
• Do not add any chemical addi- tives. Engine oil also lubricates
the clutch and additives could
cause clutch slippage.
• Do not allow foreign material to enter the crankcase.
(Except for USA and CDN)
• Do not add any chemical addi-tives or use oils with a grade of
CD "a" or higher.
• Do not use oils labeled "ENERGY CONSERVING II" "b" or higher.
Engine oil also lubricates the
clutch and additives could cause
clutch slippage.
• Do not allow foreign material to enter the crankcase.
4. Install:
• Oil tank cap
5. Start the engine and let it warm up for several minutes.
6. Turn off the engine and inspect the oil level once again.
Wait a few minutes until the oil settles
before inspecting the oil level.
CHANGING THE ENGINE OIL
1. Start the engine and warm it up for several minutes, and then turn
off the engine and wait for five
minute.
2. Place the machine on a level place and hold it on upright posi-
tion by placing the suitable stand
under the engine.
3. Place a suitable container under
the engine.
Recommended oil:Yamalube 4,
SAE10W30 or
SAE20W40
Yamalube 4-R,
SAE10W50
API service SG type or
higher, JASO standard
MA
Recommended oil: SAE10W30,
SAE10W40,
SAE15W40, SAE20W40
or SAE20W50
API service SG type or
higher, JASO standard
MA

4-4
ENGINE
EXAMPLES OF CARBURETOR SETTING DEPENDING ON SYMPTOM
* This should be taken simply for an example. It is necessary to set the carburetor while checking the operating conditions
of the engine.
Symptom Setting Checking
At full throttle Hard breathing
Shearing noise
Whitish spark plug ↓
Lean mixture Increase main jet calibration no. (Gradual-
ly)
Discoloration of spark plug
→If tan color, it
is in good condition.
If cannot be corrected: Clogged float valve seat
Clogged fuel hose
Clogged fuel cock
Check that the accelerator pump operates
smoothly.
At full throttle Speed pick-up stops
Slow speed pick-up
Slow response
Sooty spark plug ↓
Rich mixture Decrease main jet calibration no. (Gradual-
ly)
Discoloration of spark plug
→If tan color, it
is in good condition.
If cannot be corrected: Clogged air filter
Fuel overflow from carburetor
Lean mixture Lower jet needle clip position. (1 groove
down)
The clip position is the jet needle groove on
which the clip is installed.
The positions are numbered from the top.
Check that the accelerator pump operates
smoothly. (except for rich mixture symp-
tom).
Rich mixture
Raise jet needle clip position. (1 groove up)
1/4–3/4 throttle Hard breathing
Lack of speed Lower jet needle clip position. (1 groove
down)
1/4–1/2 throttle Slow speed pick-up
Poor acceleration Raise jet needle clip position. (1 groove up)
Closed to 1/4 throttle Hard breathing
Speed down Use jet needle with a smaller diam
eter. Slow-speed-circuit passage
Clogged→Clean.
Overflow from carburetor
Closed to 1/4 throttle Poor acceleration Use jet needle with a larger diameter.
Raise jet needle clip position. (1 groove up)
Poor response in the low to in-
termediate speeds Raise jet needle clip position.
If this has no effect, lower the jet needle clip
position.
Poor response when throttle is
opened quickly Check overall settings.
Use main jet with a lower calibration no.
Raise jet needle clip position. (1 groove up)
If these have no effect, use a main jet with
a higher calibration no. and lower the jet
needle clip position. Check air filter for fouling.
Check that the accelerator pump operates
smoothly.
Jet needleClip
Groove 7 Groove 6
Groove 5
Groove 4
Groove 3
Groove 2
Groove 1
Leaner
(Standard) Richer

5-4
CARBURETOR
CARBURETOR
REMOVING THE CARBURETOROrder Part name Q'ty Remarks Seat and fuel tank Refer to "REMOVING THE SEAT, FUEL
TANK AND SIDE COVERS" section in the
CHAPTER 3.
Rear shock absorber Refer to "REAR SHOCK ABSORBER" sec-
tion in the CHAPTER 6.
1Clamp 2
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)
2 Nm (0.2 m kg, 1.4 ft lb)
11 Nm (1.1 m kg, 8.0 ft lb)
4 Nm (0.4 m kg, 2.9 ft lb)
10 Nm (1.0 m kg, 7.2 ft lb)
3 Nm (0.3 m kg, 2.2 ft lb)
3 Nm (0.3 m kg, 2.2 ft lb)

5-7
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" • Main air jet "7"
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. 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 ca rburetor 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.
Float height:
8.0 mm (0.31 in)

5-10
CARBURETOR
17. Install:• Throttle valve assembly "1"
• Screw (throttle shaft) "2"
Install the valve lever rollers "3" into
the slits "a" of the throttle valve.
18. Install:• O-ring "1"
• Valve lever housing cover "2"
• Bolt (valve lever housing cover) "3"
19. 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"
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)

5-12
AIR INDICTOIN SYSTEM
AIR INDICTOIN SYSTEM
REMOVING THE AIR INDUCTION SYSTEMOrder Part name Q'ty Remarks1 Bracket 1
2 Air cut-off valve assembly 1
3 Air induction hose (air cut-off valve - front of cyl-
inder head) 1
4 Air induction pipe 1
5 Gasket 1
6 Air induction hose (air cut-off valve - rear of cylin-
der head)
1
7 Air induction hose (air cut-off valve - air filter
case) 1
7 Nm (0.7 m kg, 5.1 ft lb)10 Nm (1.0 m kg, 7.2 ft lb)
4 Nm (0.4 m kg, 2.9 ft lb)

5-13
AIR INDICTOIN SYSTEM
CHECKING THE AIR INDUCTION
SYSTEM
1. Inspect:• Air induction hose
Crack/damage →Replace.
• Air induction pipe Crack/damage →Replace.
2. Check: • Operation of air cut valvePass air through the pipe and
check the air cut valve for opera-
tion.
Does not meet the following con-
dition →Replace the air cut valve
assembly.
• Blow in air to check for operation.
• When using vacuum, check by the use of the vacuum/pressure pump
gauge set "1".
When using vacuum on the pipe
"c", take care not to exceed the
specified value.
a. From air filter
b. To cylinder head (exhaust
port)
c. From cylinder head (intake port)
A. Check for induction from air filter.
B. Check for prevention of back-
flow into air filter.
C. Check for prevention of after- burn. (When throttle is closed
at sudden deceleration)
"a" to "b" Air passes.
"b" to "a" Air does not pass.
"a" to "b"
Air does not pass
when specified pres-
sure is on "c".
Vacuum/pressure pump
gauge set: YB-35956-A/90890-
06756
Vacuum specifying pres-
sure: 46.7–86.7 kPa (350–650
mmHg, 13.8–25.6 inHg)