stop start YAMAHA YZ450F 2008 Owners Manual

1-1
DESCRIPTION
GENERAL INFORMATION
DESCRIPTION
• The machine you have purchased may differ slightly from those shown in the following.
• Designs and specifications are subject to change without notice.
1. Clutch lever
2. Hot starter lever
3. Front brake lever
4. Throttle grip
5. Radiator cap
6. Fuel tank cap
7. Engine stop switch
8. Kickstarter crank
9. Fuel tank
10. Radiator11. Coolant drain bolt
12. Rear brake pedal
13. Valve joint
14. Fuel cock
15. Cold starter knob
16. Drive chain
17. Air cleaner
18. Shift pedal
19. Oil dipstick
20. Front fork
1

1-8
CONTROL FUNCTIONS
CONTROL FUNCTIONS
ENGINE STOP SWITCH
The engine stop switch "1" is located
on the left handlebar. Continue push-
ing the engine stop switch till the en-
gine comes to a stop.
CLUTCH LEVER
The clutch lever "1" is located on the
left handlebar; it disengages or en-
gages the clutch. Pull the clutch lever
to the handlebar to disengage the
clutch, and release the lever to en-
gage the clutch. The lever should be
pulled rapidly and released slowly for
smooth starts.
SHIFT PEDAL
The gear ratios of the constant-mesh
5 speed transmission are ideally
spaced. The gears can be shifted by
using the shift pedal "1" on the left
side of the engine.
KICKSTARTER CRANK
Rotate the kickstarter crank "1" away
from the engine. Push the starter
down lightly with your foot until the
gears engage, then kick smoothly
and forcefully to start the engine. This
model has a primary kickstarter crank
so the engine can be started in any
gear if the clutch is disengaged. In
normal practices, however, shift to
neutral before starting.THROTTLE GRIP
The throttle grip "1" is located on the
right handlebar; it accelerates or de-
celerates the engine. For accelera-
tion, turn the grip toward you; for
deceleration, turn it away from you.
FRONT BRAKE LEVER
The front brake lever "1" is located on
the right handlebar. Pull it toward the
handlebar to activate the front brake.
REAR BRAKE PEDAL
The rear brake pedal "1" is located on
the right side of the machine. Press
down on the brake pedal to activate
the rear brake.
FUEL COCK
The fuel cock supplies fuel from the
tank to carburetor and also filters the
fuel. The fuel cock has the two posi-
tions:
OFF:
With the lever in this position, fuel will
not flow. Always return the lever to
this position when the engine is not
running.
ON:
With the lever in this position, fuel
flows to the carburetor. Normal riding
is done with the lever in this position.COLD STARTER KNOB
When cold, the engine requires a
richer air-fuel mixture for starting. A
separate starter circuit, which is con-
trolled by the cold starter knob "1",
supplies this mixture. Pull the cold
starter knob out to open the circuit for
starting. When the engine has
warmed up, push it in to close the cir-
cuit.
HOT STARTER LEVER
The hot starter lever "1" is used when
starting a warm engine. Use the hot
starter lever when starting the engine
again immediately after it was
stopped (the engine is still warm).
Pulling the hot starter lever injects
secondary air to thin the air-fuel mix-
ture temporarily, allowing the engine
to be started more easily.
STARTING AND BREAK-IN
FUEL
Always use the recommended fuel as
stated below. Also, be sure to use
new gasoline the day of a race.
Use only unleaded gasoline. The
use of leaded gasoline will cause
severe damage to the engine inter-
nal parts such as valves, piston
rings, and exhaust system, etc.
Recommended fuel:
Premium unleaded
gasoline only with a re-
search octane number
of 95 or higher.

1-9
STARTING AND BREAK-IN
If knocking or pinging occurs, use a
different brand of gasoline or higher
octane grade.
• For refueling, be sure to stop the
engine and use enough care not
to spill any fuel. Also be sure to
avoid refueling close to a fire.
• Refuel after the engine, exhaust
pipe, etc. have cooled off.
HANDLING NOTE
Never start or run the engine in a
closed area. The exhaust fumes
are poisonous; they can cause
loss of consciousness and death
in a very short time. Always oper-
ate the machine in a well-ventilated
area.
• The carburetor on this machine
has a built-in accelerator pump.
Therefore, when starting the en-
gine, do not operate the throttle
or the spark plug will foul.
• Unlike a two-stroke engine, this
engine cannot be kick started
when the throttle is open be-
cause the kickstarter may kick
back. Also, if the throttle is open
the air/fuel mixture may be too
lean for the engine to start.
• Before starting the machine, per-
form the checks in the pre-opera-
tion check list.
STARTING A COLD ENGINE
1. Inspect the coolant level.
2. Turn the fuel cock to "ON".
3. Shift the transmission into neutral.
4. Fully open the cold starter knob
"1".
5. Kick the kickstarter crank.
Do not open the throttle while kick-
ing the kickstarter crank. Other-
wise, the kickstarter crank may
kick back.
6. Return the cold starter knob to its
original position and run the en-
gine at 3,000–5,000 r/min for 1 or
2 minutes.
Since this model is equipped with an
accelerator pump, if the engine is
raced (the throttle opened and
closed), the air/fuel mixture will be too
rich and the engine may stall. Also
unlike a two-stroke engine, this model
can idle.
Do not warm up the engine for ex-
tended periods of time.
STARTING A WARM ENGINE
Do not operate the cold starter knob
and throttle. Pull the hot starter lever
"1" and start the engine by kicking
the kickstarter crank forcefully with a
firm stroke. As soon as the engine
starts, release the hot starter lever to
close the air passage.
Restarting an engine after a fall
Pull the hot starter lever and start the
engine. As soon as the engine starts,
release the hot starter lever to close
the air passage.The engine fails to start
Pull the hot starter lever all the way
out and while holding the lever, kick
the kickstarter crank 10 to 20 times to
clear the engine. Then, restart the en-
gine. Refer to "Restarting an engine
after a fall".
Observe the following break-in
procedures during initial operation
to ensure optimum performance
and avoid engine damage.
BREAK-IN PROCEDURES
1. Before starting the engine, fill the
fuel tank with the fuel.
2. Perform the pre-operation checks
on the machine.
3. Start and warm up the engine.
Check the idle speed, and check
the operation of the controls and
Thrott
le
grip
oper-
ation*Cold
start-
er
knobHot
start-
er le-
ver
Star
ting
a
cold
en-
gineAir tem-
perature =
less than
5 °C (41
°F)Open
3 or 4
timesON OFF
Air tem-
perature =
more than
5 °C (41
°F)None ON OFF
Air tem-
perature
(normal
tempera-
ture) = be-
tween 5
°C (41 °F)
and 25 °C
(77 °F)NoneON/
OFFOFF
Air tem-
perature =
more than
25 °C (77
°F)None OFF OFF
Starting an en-
gine after a long
period of timeNone ON OFF
Restarting a
warm engineNone OFF ON
Restarting an
engine after a
fallNone OFF ON
* Operate the throttle grip before kick
starting.

1-10
STARTING AND BREAK-IN
the engine stop switch. Then, re-
start the engine and check its op-
eration within no more than 5
minutes after it is restarted.
4. Operate the machine in the lower
gears at moderate throttle open-
ings for five to eight minutes.
5. Check how the engine runs when
the machine is ridden with the
throttle 1/4 to 1/2 open (low to me-
dium speed) for about one hour.
6. Restart the engine and check the
operation of the machine through-
out its entire operating range. Re-
start the machine and operate it
for about 10 to 15 more minutes.
The machine will now be ready to
race.
• After the break-in or before each
race, you must check the entire
machine for loose fittings and
fasteners as per "TORQUE-
CHECK POINTS". Tighten all
such fasteners as required.
• When any of the following parts
have been replaced, they must
be broken in.
CYLINDER AND CRANKSHAFT:
About one hour of break-in oper-
ation is necessary.
PISTON, RING, VALVES, CAM-
SHAFTS AND GEARS:
These parts require about 30
minutes of break-in operation at
half-throttle or less. Observe the
condition of the engine carefully
during operation.

1-12
CLEANING AND STORAGE
CLEANING AND STORAGE
CLEANING
Frequent cleaning of your machine
will enhance its appearance, maintain
good overall performance, and ex-
tend the life of many components.
1. Before washing the machine,
block off the end of the exhaust
pipe to prevent water from enter-
ing. A plastic bag secured with a
rubber band may be used for this
purpose.
2. If the engine is excessively
greasy, apply some degreaser to
it with a paint brush. Do not apply
degreaser to the chain, sprockets,
or wheel axles.
3. Rinse the dirt and degreaser off
with a garden hose; use only
enough pressure to do the job.
Excessive hose pressure may
cause water seepage and contami-
nation of wheel bearings, front
forks, brakes and transmission
seals. Many expensive repair bills
have resulted from improper high
pressure detergent applications
such as those available in coin-op-
erated car washers.
4. After the majority of the dirt has
been hosed off, wash all surfaces
with warm water and a mild deter-
gent. Use an old toothbrush to
clean hard-to-reach places.
5. Rinse the machine off immediate-
ly with clean water, and dry all
surfaces with a soft towel or cloth.
6. Immediately after washing, re-
move excess water from the
chain with a paper towel and lubri-
cate the chain to prevent rust.
7. Clean the seat with a vinyl uphol-
stery cleaner to keep the cover
pliable and glossy.
8. Automotive wax may be applied
to all painted or chromed surfac-
es. Avoid combination cleaner-
waxes, as they may contain abra-
sives.
9. After completing the above, start
the engine and allow it to idle for
several minutes.
STORAGE
If your machine is to be stored for 60
days or more, some preventive mea-
sures must be taken to avoid deterio-
ration. After cleaning the machine
thoroughly, prepare it for storage as
follows:
1. Drain the fuel tank, fuel lines, and the carburetor float bowl.
2. Remove the spark plug, pour a ta-
blespoon of SAE 10W-30 motor
oil in the spark plug hole, and re-
install the plug. With the engine
stop switch pushed in, kick the en-
gine over several times to coat the
cylinder walls with oil.
3. Remove the drive chain, clean it
thoroughly with solvent, and lubri-
cate it. Reinstall the chain or store
it in a plastic bag tied to the frame.
4. Lubricate all control cables.
5. Block the frame up to raise the
wheels off the ground.
6. Tie a plastic bag over the exhaust
pipe outlet to prevent moisture
from entering.
7. If the machine is to be stored in a
humid or salt-air environment,
coat all exposed metal surfaces
with a film of light oil. Do not apply
oil to rubber parts or the seat cov-
er.
Make any necessary repairs before
the machine is stored.

2-11
TIGHTENING TORQUES
Throttle cable (return) M12 × 1.0 1 11 1.1 8.0
Throttle cable cover M5 × 0.8 2 4 0.4 2.9
Hot starter plunger M12 × 1.0 1 2 0.2 1.4
Hot starter cable adjust bolt and locknut M6 × 0.75 1 4 0.4 2.9
Air filter element M6 × 1.0 1 2 0.2 1.4
Radiator stay M6 × 1.0 6 7 0.7 5.1
Radiator M6 × 1.0 4 10 1.0 7.2
Radiator hose clamp M6 × 1.0 8 2 0.2 1.4
Radiator pipe 1, 2 M6 × 1.0 2 10 1.0 7.2
Impeller M8 × 1.25 1 14 1.4 10
Water pump housing cover M6 × 1.0 3 10 1.0 7.2
Coolant drain bolt M6 × 1.0 1 10 1.0 7.2
Oil pump cover M4 × 0.7 1 2 0.2 1.4
Oil pump M6 × 1.0 2 10 1.0 7.2
Oil pump drive gear shaft M6 × 1.0 1 10 1.0 7.2
Oil filter element drain bolt M6 × 1.0 1 10 1.0 7.2
Oil filter element cover M6 × 1.0 2 10 1.0 7.2
Oil pressure check bolt M6 × 1.0 1 10 1.0 7.2
△Oil hose clamp — 2 2 0.2 1.4
Crankshaft end accessing screw M27 × 1.5 1 10 1.0 7.2
Timing mark accessing screw M14 × 1.5 1 6 0.6 4.3
Clutch cover M6 × 1.0 7 10 1.0 7.2
Right crankcase cover M6 × 1.0 8 10 1.0 7.2
Right crankcase cover M6 × 1.0 2 12 1.2 8.7
Left crankcase cover M6 × 1.0 8 10 1.0 7.2
Crankcase M6 × 1.0 12 12 1.2 8.7
Clutch cable holder M6 × 1.0 2 10 1.0 7.2
Oil drain bolt (right crankcase) M10 × 1.25 1 20 2.0 14
Oil drain bolt (left crankcase) M8 × 1.25 1 20 2.0 14
Oil check bolt (crankcase) M6 × 1.0 1 10 1.0 7.2
Oil strainer M6 × 1.0 1 10 1.0 7.2
Crankcase bearing stopper M6 × 1.0 8 10 1.0 7.2
Crankcase bearing stopper (crankshaft) M6 × 1.0 4 14 1.4 10
Drive axle oil seal stopper M6 × 1.0 2 10 1.0 7.2
Kick shaft ratchet wheel guide M6 × 1.0 2 12 1.2 8.7
Kickstarter crank M8 × 1.25 1 33 3.3 24
Screw (kickstarter crank) M6 × 1.0 1 7 0.7 5.1
Primary drive gear M20 × 1.0 1 110 11.0 80
Clutch boss M20 × 1.0 1 75 7.5 54
Clutch cable adjust bolt and locknut M6 × 0.75 1 4 0.4 2.9
Clutch spring M6 × 1.0 6 10 1.0 7.2
Balancer M10 × 1.0 1 45 4.5 32
Balancer shaft driven gear M14 × 1.0 1 50 5.0 36
Balancer weight M6 × 1.0 3 10 1.0 7.2Part to be tightened Thread size Q'tyTightening torque
Nm m•kg ft•lb

2-12
TIGHTENING TORQUES
*1: Tighten the cylinder head bolts to 30 Nm (3.0 m • kg, 22 ft • lb) in the proper tightening sequence, remove and retighten
the cylinder head bolts to 20 Nm (2.0 m • kg, 14 ft • lb) in the proper tightening sequence, and then tighten the cylinder head
bolts further to reach the specified angle 180° in the proper tightening sequence.
CHASSIS
△- marked portion shall be checked for torque tightening after break-in or before each race.
Drive sprocket M20 × 1.0 1 75 7.5 54
Drive chain sprocket cover M6 × 1.0 2 8 0.8 5.8
Shift pedal M6 × 1.0 1 12 1.2 8.7
Shift guide M6 × 1.0 2 10 1.0 7.2
Stopper lever M6 × 1.0 1 10 1.0 7.2
Segment M8 × 1.25 1 30 3.0 22Part to be tightened Thread size Q'tyTightening torque
Nm m•kg ft•lb
Part to be tightened Thread size Q'tyTightening torque
Nm m•kg ft•lb
△Upper bracket and outer tube M8 × 1.25 4 21 2.1 15
△Lower bracket and outer tube M8 × 1.25 4 21 2.1 15
△Upper bracket and steering stem M24 × 1.0 1 145 14.5 105
△Handlebar upper holder M8 × 1.25 4 28 2.8 20
△Handlebar lower holder M10 × 1.25 2 34 3.4 24
△Steering ring nut M28 × 1.0 1 Refer to NOTE.
Front fork and damper assembly M51 × 1.5 2 30 3.0 22
Front fork and adjuster M22 × 1.25 2 55 5.5 40
Damper assembly and base valve M42 × 1.5 2 29 2.9 21
Adjuster and damper assembly M12 × 1.25 2 29 2.9 21
Bleed screw (front fork) and base valve M5 × 0.8 2 1 0.1 0.7
△Front fork and front fork protector M6 × 1.0 6 5 0.5 3.6
△Front fork protector and brake hose holder M6 × 1.0 2 7 0.7 5.1
Throttle grip cap M5 × 0.8 2 4 0.4 2.9
Clutch lever holder M5 × 0.8 2 4 0.4 2.9
Clutch lever mounting nut M6 × 1.0 1 4 0.4 2.9
Hot starter lever holder M5 × 0.8 2 4 0.4 2.9
△Front brake master cylinder and bracket M6 × 1.0 2 9 0.9 6.5
Front brake master cylinder cap M4 × 0.7 2 2 0.2 1.4
Brake lever mounting bolt M6 × 1.0 1 6 0.6 4.3
Brake lever mounting nut M6 × 1.0 1 6 0.6 4.3
Brake lever position locknut M6 × 1.0 1 5 0.5 3.6
△Cable guide (front brake hose) and under bracket M6 × 1.0 1 4 0.4 2.9
△Front brake hose union bolt (brake master cylinder) M10 × 1.25 1 30 3.0 22
△Front brake hose union bolt (brake caliper) M10 × 1.25 1 30 3.0 22
△Front brake caliper and front fork M8 × 1.25 2 28 2.8 20
△Brake caliper (front and rear) and pad pin plug M10 × 1.0 2 3 0.3 2.2
△Brake caliper (front and rear) and pad pin M10 × 1.0 2 18 1.8 13
△Brake caliper (front and rear) and bleed screw M8 × 1.25 2 6 0.6 4.3

2-20
CABLE ROUTING DIAGRAM
1. Hot starter cable
2. Clamp
3. Throttle position sensor lead
4. Hump (frame)
5. Neutral switch lead
6. Engine bracket
7. Lower engine guard stay
8. CDI magneto lead
9. Clutch cable
10. Radiator breather hose
11. Radiator hose 212. Engine stop switch lead
13. Sub-wire harness
14. Ground lead
15. CDI unit bracket
16. CDI unit
17. Cable guide
18. Ignition coil lead
19. Throttle cableA. Fasten the hot starter cable and
throttle cables onto the frame.
Locate the clamp ends under
the hot starter cable.
B. Fasten the hot starter cable,
throttle cables, throttle position
sensor lead and ignition coil lead
to the frame.
C. Pass the throttle position sensor
lead over the hot starter cable.

2-24
CABLE ROUTING DIAGRAM
1. Throttle cable
2. Clamp
3. Hot starter cable
4. Clutch cable
5. Engine stop switch lead
6. Cable guide
7. Brake hose
8. Hose guide
A. Fasten the engine stop switch
lead to the handlebar.B. Pass the clutch cable and hot
starter cable through the cable
guide.
C. Pass the brake hose in front of
the number plate.
D. Pass the throttle cables through
the cable guide.
E. Pass the clutch cable and hot
starter cable through the cable
guide on the number plate.

3-5
ENGINE
ENGINE
CHECKING THE COOLANT LEVEL
Do not remove the radiator cap
"1", drain bolt and hoses when the
engine and radiator are hot. Scald-
ing hot fluid and steam may be
blown out under pressure, which
could cause serious injury. When
the engine has cooled, place a
thick towel over the radiator cap,
slowly rotate the cap counter-
clockwise to the detent. This pro-
cedure allows any residual
pressure to escape. When the
hissing sound has stopped, press
down on the cap while turning
counterclockwise and remove it.
Hard water or salt water is harmful
to the engine parts. You may use
distilled water, if you can't get soft
water.
1. Place the machine on a level
place, and hold it in an upright po-
sition.
2. Remove:
• Radiator cap
3. Check:
• Coolant level "a"
Coolant level low
→Add coolant.
1. Radiator
CHANGING THE COOLANT
Do not remove the radiator cap
when the engine is hot.
Take care so that coolant does not
splash on painted surfaces. If it
splashes, wash it away with water.
1. Place a container under the en-gine.
2. Remove:
• Engine guard "1"
• Coolant drain bolt "2"
3. Remove:
• Radiator cap
Drain the coolant completely.
4. Clean:
• Cooling system
Thoroughly flush the cooling sys-
tem with clean tap water.
5. Install:
• Copper washer
• Coolant drain bolt
• Engine guard
• Bolt (engine guard)
6. Fill:
• Radiator
•Engine
To specified level.
• Do not mix more than one type of
ethylene glycol antifreeze con-
taining corrosion inhibitors for
aluminum engine.
• Do not use water containing im-
purities or oil.
Handling notes of coolant:
The coolant is harmful so it should be
handled with special care.
• When coolant splashes to your
eye.
Thoroughly wash your eye with
water and see your doctor.
• When coolant splashes to your
clothes.
Quickly wash it away with water
and then with soap.
• When coolant is swallowed.
Quickly make him vomit and take
him to a doctor.
7. Install:
• Radiator cap
Start the engine and warm it up
for a several minutes.
8. Check:
• Coolant level
Coolant level low
→Add coolant.
CHECKING THE RADIATOR CAP
1. Inspect:
• Seal (radiator cap) "1"
• Valve and valve seat "2"
Crack/damage
→Replace.
Exist fur deposits "3"
→Clean or
replace.
CHECKING THE RADIATOR CAP
OPENING PRESSURE
1. Attach:
• Radiator cap tester "1" and adapt-
er "2"
Coolant drain bolt:
10 Nm (1.0 m•kg, 7.2
ft•lb)
Bolt (engine guard):
10 Nm (1.0 m•kg, 7.2
ft•lb)
Recommended coolant:
High quality ethylene
glycol anti-freeze con-
taining anti-corrosion
for aluminum engine
Coolant "1" and water
(soft water) "2" mixing ra-
tio:
50%/50%
Coolant capacity:
0.99 L (0.87 Imp qt, 1.05
US qt)
Radiator cap tester:
YU-24460-01/90890-
01325
Radiator cap tester
adapter:
YU-33984/90890-01352