YAMAHA WR 250F 2008 Manual Online

3-26
CHASSIS
LUBRICATION
To ensure smooth operation of all
components, lubricate your machine
during setup, after break-in, and after
every race.
1. All control cable
2. Clutch lever pivot
3. Shift pedal pivot
4. Footrest pivot
5. Throttle-to-handlebar contact
6. Drive chain
7. Tube guide cable winding por-tion
8. Throttle cable end
9. Clutch cable end
10. Hot starter cable end
A. Use Yamaha cable lube or equivalent on these areas. B. Use SAE 10W-30 motor oil or
suitable chain lubricants.
C. Lubricate the following areas
with high quality, lightweight lith-
ium-soap base grease.
Wipe off any excess grease, and
avoid getting grease on the brake
discs.

3-27
ELECTRICAL
ELECTRICAL
CHECKING THE SPARK PLUG
1. Remove:• Spark plug
2. Inspect:
• Electrode "1"Wear/damage →Replace.
• Insulator color "2"
Normal condition is a medium to
light tan color.
Distinctly different color →Check
the engine condition.
When the engine runs for many hours
at low speeds, the spark plug insula-
tor will become sooty, even if the en-
gine and carburetor are in good
operating condition.
3. Measure: • Plug gap "a"Use a wire gauge or thickness
gauge.
Out of specification →Regap.
4. Clean the plug with a spark plug cleaner if necessary.
5. Tighten: • Spark plug
• Before installing a spark plug, clean the gasket surface and plug sur-
face.
• Finger-tighten "a" the spark plug before torquing to specification "b".
CHECKING THE IGNITION TIMING
1. Remove:• Timing mark accessing screw "1"
2. Attach: • Timing light
• Inductive tachometerTo the ignition coil lead (orange
lead"1").
3. Adjust: • Engine idling speedRefer to "ADJUSTING THE EN-
GINE IDLING SPEED" section.
4. Check: • Ignition timingVisually check the stationary
pointer "a" is within the firing
range "b" on the rotor.
Incorrect firing range →Check ro-
tor and pickup assembly.
5. Install: • Timing mark accessing screw
CHECKING AND CHARGING THE
BATTERY
Batteries generate explosive hy-
drogen gas and contain electrolyte
which is made of poisonous and
highly caustic sulfuric acid. There-
fore, always follow these preven-
tive measures:
• Wear protective eye gear when handling or working near batter-
ies. • Charge batteries
in a well-venti-
lated area.
• Keep batteries away from fire, sparks or open flames (e.g.,
welding equipment, lighted ciga-
rettes).
• DO NOT SMOKE when charging
or handling batteries.
• KEEP BATTERIES AND ELEC- TROLYTE OUT OF REACH OF
CHILDREN.
• Avoid bodily contact with elec- trolyte as it can cause severe
burns or permanent eye injury.
FIRST AID IN CASE OF BODILY
CONTACT:
EXTERNAL
• Skin — Wash with water.
• Eyes — Flush with water for 15
minutes and get immediate med-
ical attention.
INTERNAL
• Drink large quantities of water or milk followed with milk of magne-
sia, beaten egg or vegetable oil.
Get immediate medical attention.
Charging time, charging amperage
and charging voltage for an MF
battery are different from those of
conventional batteries. The MF
battery should be charged as ex-
plained in the charging method il-
lustrations. If the battery is
overcharged, the electrolyte level
will drop considerably. Therefore,
take special care when charging
the battery.
Since MF batteries are sealed, it is
not possible to check the charge state
of the battery by measuring the spe-
cific gravity of the electrolyte. There-
fore, the charge of the battery has to
be checked by measuring the voltage
at the battery terminals.
1. Remove:• Seat
2. Disconnect:
• Battery leads(from the battery terminals)
First, disconnect the negative bat-
tery lead "1", and then the positive
battery lead "2".
Spark plug gap: 0.7–0.8 mm (0.028–
0.031 in)
Spark plug: 13 Nm (1.3 m•kg, 9.4
ft•lb)
Timing light:
YM-33277-A/90890-
03141

3-28
ELECTRICAL
3. Remove:• Battery band
•Battery
4. Measure: • Battery charge
Measurement steps:
a. Connect a pocket tester "1" to the
battery terminals.
• The charge state of an MF battery can be checked by measuring its
open-circuit voltage (i.e., the volt-
age when the positive terminal is
disconnected).
• No charging is necessary when the
opencircuit voltage equals or ex-
ceeds 12.8 V.
b. Check the charge of the battery,
as shown in the charts and the fol-
lowing example.
Example
Open-circuit voltage = 12.0 V
Charging time = 6.5 hours
Charge of the battery = 20–30%
A. Relationship between the open-circuit voltage and the
charging time at 20 °C (68 °F)
(These values vary with the
temperature, t he condition of
the battery plates, and the
electrolyte level.)
B. Open-circuit voltage
C. Charging time (hours)
D. Time (minutes)
E. Charging condition of the bat-
tery
F. Ambient temperature 20 °C (68 °F)
a. Charging
b. Check the open-circuit volt- age
5. Charge: •Battery(refer to the appropriate charging
method illustration)
Do not quick charge a battery.
• Never remove the MF battery sealing caps.
• Do not use a high-rate battery charger since it forces a high-
amperage current into the bat-
tery quickly and can cause bat-
tery overheating and battery
plate damage.
• If it is impossible to regulate the charging current on the battery
charger, be careful not to over-
charge the battery.
• When charging a battery, be sure
to remove it from the machine. (If
charging has to be done with the
battery mounted on the machine,
disconnect the negative battery
lead from the battery terminal.) • To reduce the chance of sparks,
do not plug in the battery charger
until the battery charger leads
are connected to the battery.
• Before removing the battery charger lead clips from the bat-
tery terminals, be sure to turn off
the battery charger.
• Make sure the battery charger lead clips are in full contact with
the battery terminal and that they
are not shorted. A corroded bat-
tery charger lead clip may gener-
ate heat in the contact area and a
weak clip spring may cause
sparks.
• If the battery becomes hot to the touch at any time during the
charging process, disconnect
the battery char ger and let the
battery cool before reconnecting
it. Hot batteries can explode!
• As shown in the following illus- tration, the open-circuit voltage
of an MF battery stabilizes about
30 minutes after charging has
been completed. Therefore, wait
30 minutes after charging is com-
pleted before measuring the
open-circuit voltage.
Tester positive probe →battery
positive terminal
Tester negative probe →battery
negative terminal

3-29
ELECTRICAL
Charging method using a variable voltage charger

3-30
ELECTRICAL
Charging method using a constant voltage charger

3-31
ELECTRICAL
6. Install:•Battery
• Battery band
7. Connect:
• Battery leads(to the battery terminals)
First, connect the positive lead "1",
then the negative lead "2".
8. Check:• Battery terminals
Dirt →Clean with a wire brush.
Loose connection →Connect
properly.
9. Lubricate: • Battery terminal
10. Install: • Seat
CHECKING THE FUSE
To avoid a short circuit, always set
the main switch to "OFF" when
checking or replacing a fuse.
1. Remove: • Seat
• Fuse cover
2. Check:
• Continuity
Checking steps:
a. Remove the fuse "1".
b. Connect the pocket tester to the fuse and check the continuity.
Set the pocket tester selector to " Ω×
1".
2. Reserve fuse
c. If the pocket test er indicates "∞",
replace the fuse.
3. Replace: • Blown fuse
Replacement steps:
a. Set the main switch to "OFF".
b. Install a new fuse of the correct amperage.
c. Set on the switches to verify if the electrical circuit is operational.
d. If the fuse immediately blows again, check the electrical circuit.
Never use a fuse with an amperage
rating other than th at specified. Im-
provising or using a fuse with the
wrong amperage rating may cause
extensive damage to the electrical
system, cause the starting and ig-
nition systems to malfunction and
could possibly cause a fire.
4. Install: • Fuse cover
•Seat
REPLACING THE HEADLIGHT
BULBS
1. Remove: • HeadlightRefer to "REMOVING THE SEAT,
FUEL TANK AND SIDE COV-
ERS" section.
2. Remove:
• Headlight bulb holder cover "1" 3. Remove:
• Headlight bulb holder "1"
Remove the headlight bulb holder by
pushing it in and turning it counter-
clockwise.
4. Remove:• Headlight bulb
Since the headlight bulb gets ex-
tremely hot, keep flammable prod-
ucts and your hands away from the
bulb unit it has cooled down.
5. Install:• Headlight bulb
Avoid touching the glass part of
the headlight bulb to keep it free
form oil, otherwis e the transparen-
cy of the glass, the life of the bulb
and the luminous flux will be ad-
versely affected. If the headlight
bulb gets soiled, thoroughly clean
it with a cloth moistened with alco-
hol or lacquer thinner.
6. Install: • Headlight bulb holder
7. Install:
• Headlight bulb holder cover
8. Install: • Headlight
Refer to "REMOVING THE SEAT,
FUEL TANK AND SIDE COV-
ERS" section.
Recommended lubricant:
Lithium soap base
grease
Pocket tester: YU-3112-C/90890-
03112
Items Amperage ratingQ'ty
Main fuse 10 A 1
Headlight: 7 Nm (0.7 m•kg, 5.1
ft•lb)

3-32
ELECTRICAL
ADJUSTING THE HEADLIGHT
BEAMS
1. Adjust:• Headlight beam (vertically)
Adjusting steps:
a. Turn the adjusting screw "1" in di-
rection "a" or "b".
Direction "a" Headlight beam is raised.
Direction "b" Headlight beam is lowered.

4-1
ENGINE
TUNING
ENGINE
CARBURETOR SETTING
• The air/fuel mixture will vary de-pending on atmospheric conditions.
Therefore, it is necessary to take
into consideration the air pressure,
ambient temperature, humidity,
etc., when adjusting the carburetor.
• Perform a test run to check for prop- er engine performance (e.g., throt-
tle response) and spark plug(-s)
discoloration or fouling. Use these
readings to determine the best pos-
sible carburetor setting.
It is recommended to keep a record of
all carburetor settings and external
conditions (e.g., atmospheric condi-
tions, track/surface conditions, lap
times) to make future carburetor set-
ting easier.
• The carburetor is a part of the fuel line. Therefore, be sure to in-
stall it in a wellventilated area,
away from flammable objects
and any sources of fire.
• Never look into the carburetor in- take. Flames may shoot out from
the pipe if the engine backfires
while it is being started. Gasoline
may be discharged from the ac-
celerator pump nozzle when the
carburetor has been removed.
• The carburetor is extremely sen-sitive to foreign matter (dirt,
sand, water, etc.). During instal-
lation, do not al low foreign mat-
ter to get into the carburetor.
• Always handle the carburetor and its components carefully.
Even slight scratches, bends or
damage to carburetor parts may
prevent the carburetor from
functioning correctly. Carefully
perform all servicing with the ap-
propriate tools and without ap-
plying excessive force.
• When the engine is stopped or when riding at no load, do not
open and close the throttle un-
necessarily. Otherwise, too
much fuel may be discharged,
starting may become difficult or
the engine may not run well. • After installing the carburetor,
check that the throttle operates
correctly and opens and closes
smoothly.
ATMOSPHERIC CONDITIONS AND
CARBURETOR SETTINGS
The air density (i.e., concentration of
oxygen in the air) determines the rich-
ness or leanness of the air/fuel mix-
ture.
• Higher temperature expands the air with its resultant reduced density.
• Higher humidity reduces the amount of oxygen in the air by so
much of the water vapor in the
same air.
• Lower atmospheric pressure (at a
high altitude) reduces the density of
the air.
EFFECT OF SETTING PARTS IN
RELATION TO THROTTLE VALVE
OPENING
A. Closed
B. Fully open
1. Pilot jet
2. Throttle valve cutaway
3. Jet needle
4. Main jet CONSTRUCTION OF
CARBURETOR AND SETTING
PARTS
The FLATCR carburetor has a prima-
ry main jet. This type of main jet is
perfect for racing machines since it
supplies an even flow of fuel, even at
full load. Use the main jet and the jet
needle to set the carburetor.
1. Jet needle
2. Pilot air jet
3. Needle jet
4. Main jet
5. Pilot jet
ADJUSTING THE MAIN JET
The richness of the air-fuel mixture at
full throttle can be set by changing the
main jet "1".
If the air-fuel mixture is too rich or too
lean, the engine power will drop, re-
sulting in poor acceleration.
Effects of changing the main jet
(reference)
A. Idle
B. Fully open
1. #180
2. #160
3. #170
Air
tem p. Hu-
midi- ty Air
pres- sure
(alti-
tude) Mix-
ture Set-
ting
High High Low
(high) Rich-
er Lean-
er
Low Low High
(low) Lean-
er Rich-
er
Standard main jet #170
* #160
* For EUROPE

4-2
ENGINE
ADJUSTING THE PILOT JET
The richness of the air-fuel mixture
with the throttle open 1/4 or less can
be set by adjusting the pilot jet "1".
Effects of adjusting the pilot jet
(reference)A. Idle
B. Fully open
1. #45
2. #40
3. #42
ADJUSTING THE JET NEEDLE
GROOVE POSITION
Adjusting the jet needle "1" position
affects the acceleration when the
throttle is 1/8 to 3/4 open.
1. Too rich at intermediate speeds • Rough engine operation is felt and the engine will not pick up
speed smoothly.
Step up the jet needle clip by one
groove and move down the nee-
dle to lean out the mixture.
2. Too lean at intermediate speeds • The engine breathes hard and will
not pick up speed quickly.
Step down the jet needle clip by
one groove and move up the nee-
dle to enrich the mixture. Effects of changing the jet needle
groove position (reference)
A. Idle
B. Fully open
1. No.5 groove
2. No.3 groove
3. No.4 groove
ADJUSTING THE JET NEEDLE
The jet needle is adjusted by chang-
ing it.
The jet needle setting parts, having
the same taper angle, are available in
different straight portion diameters. a. Diameter of the straight por- tion
Effects of changing the jet needle
(reference)
(Diameter of the straight portion)
Changing the diameter of the straight
portion adjusts the air-fuel mixture
when the throttle is 1/8 to 1/4 open. A. Idle
B. Fully open
RELATIONSHIP WITH THROTTLE
OPENING
The flow of the fuel through the car-
buretor main system is controlled by
the main jet and then, it is further reg-
ulated by the area between the main
nozzle and the jet needle.
The fuel flow relates to the diameter
of the straight portion of the jet needle
with the throttle 1/8 to 1/4 open and
relates to the clip position with the
throttle 1/8 to 3/4 open.
Therefore, the fuel flow is balanced at
each stage of throttle opening by the
combination of the jet needle straight
portion diameter and clip position. ADJUSTING THE LEAK JET
(ADJUSTING THE ACCELERATOR
PUMP)
The leak jet "1" is a setting part that
adjusts the flow of fuel discharged by
the accelerator pump. Since the ac-
celerator pump operates only when
throttle is open, the leak jet is used to
adjust a fuel mixture ratio for quick
throttle opening and is therefore dif-
ferent from other setting parts that ad-
just a fuel mixtur
e for each throttle
opening (each engine speed).
1. When the engine breathes hard in quick throttle opening, select a
leak jet having lower calibrating
No. than standard to enrich the
mixture. #70 →#65
2. When rough engine operation is
felt in quick throttle opening, se-
lect a leak jet having higher cali-
brating No. than standard to lean
out the mixture. #70
→#85
Standard pilot jet
#42
* #45
* For EUROPE
Standard clip posi- tion No.4
groove
Supplied jet needle GDEPR
* GDEPS
* For EUROPE
Standard leak jet #70
4

4-3
ENGINE
CARBURETOR SETTING PARTSMain jet Size Part
number
(-14943-)
Rich #182 4MX-94 #180 4MX-43
#178 4MX-93
#175 4MX-42
#172 4MX-92
(STD) #170 4MX-41 #168 4MX-91
#165 4MX-40
#162 4MX-90
* (STD) #160 4MX-39 Lean #158 4MX-89
Pilot jet Size Part
number
(-14948-)
Rich #50 4MX-07 #48 4MX-06
* (STD) #45 4MX-05 (STD) #42 4MX-04 Lean #40 4MX-03
Jet needle Size Part
number
(-14916-)
Rich GDEPN 5UM-BN GDEPP 5UM-BP
GDEPQ 5UM-B1 GDEPR 5UM-BRGDEPS 5UM-BS GDEPT 5UM-BT
GDEPU 5UM-BU
Lean GDEPV 5UM-BV
Leak jet Size Part
number
(-1494F-)
Rich #60 4JT-11
(STD) #70 4JT-15 #80 4JT-19
#90 4JT-23
#100 4JT-27
#110 4JT-29
Lean #120 4JT-31
* For EUROPE