engine YAMAHA YFZ450 2008 Service Manual

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3. If the coolant is at or below the minimum level
mark, remove panel A. (See page 8-9.)
4. Remove the reservoir cap, add coolant or dis-
tilled water to the maximum level mark, install
the reservoir cap, and then install the panel.CAUTION:
ECB00400

If coolant is not available, use distilled water
or soft tap water instead. Do not use hard wa-
ter or salt water since it is harmful to the en-
gine.

If water has been used instead of coolant, re-
place it with coolant as soon as possible,
otherwise the engine may not be sufficiently
cooled and the cooling system will not be
protected against frost and corrosion.

If water has been added to the coolant, have
a Yamaha dealer check the antifreeze con-
tent of the coolant as soon as possible, oth-
erwise the effectiveness of the coolant will
be reduced.
NOTE:

If the engine overheats, see page 8-52 for further
instructions.
EBU23560
To change the coolant
WARNING

EWB01890
Wait for the engine and radiator to cool before
1. Maximum level mark
2. Minimum level mark
3. Coolant reservoir
4. Coolant reservoir cap
Coolant reservoir capacity (up to the maximum
level mark):
0.29 L (0.31 US qt) (0.26 Imp.qt)
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removing the radiator cap. You could be
burned by hot fluid and steam blown out under
pressure. Always place a thick rag over the cap
when opening. Allow any remaining pressure
to escape before completely removing the cap.
1. Place the ATV on a level surface.
2. Remove panel A. (See page 8-9.)
3. Place a container under the engine, and then
remove the coolant drain bolt. (Use a trough
or a similar object as shown.)
4. Remove the radiator cap.5. Remove the coolant reservoir by removing the
bolts.
6. Remove the coolant reservoir cap, and then
turn the coolant reservoir upside down to
empty it.
1. Coolant drain bolt
2. Trough
2 1

1. Radiator cap
1

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otherwise the engine may not be sufficiently
cooled and the cooling system will not be
protected against frost and corrosion.

If water has been added to the coolant, have
a Yamaha dealer check the antifreeze con-
tent of the coolant as soon as possible, oth-
erwise the effectiveness of the coolant will
be reduced.
12. Install the radiator cap, start the engine, let it
idle for several minutes, and then turn it off.
13. Remove the radiator cap to check the coolant
level in the radiator. If it is low, add sufficient
coolant until it reaches the top of the radiator,
and then install the radiator cap.
14. Start the engine, and then check for coolant
leakage.
NOTE:

If any leakage is found, have a Yamaha dealer
check the cooling system.
15. Install the panel.
EBU23702
Cleaning the air filter element
The air filter element should be cleaned at the in-
tervals specified in the periodic maintenance andlubrication chart. Clean the air filter element more
frequently if you are riding in unusually wet or dusty
areas.
NOTE:

There is a check hose at the bottom of the air filter
case. If dust or water collects in this hose, empty
the hose and clean the air filter element and air fil-
ter case.
1. Remove the seat. (See page 4-11.)
2. Remove the air filter case cover by unhooking
the holders.
1. Air filter case check hose
1

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7. Wash the sponge material gently but thor-
oughly in solvent.
WARNING

EWB01940
Always use parts cleaning solvent to clean the
sponge material. Never use low-flash-point
solvents or gasoline to clean the sponge mate-
rial because the engine could catch fire or ex-
plode.
8. Squeeze the excess solvent out of the sponge
material and let it dry.CAUTION:

ECB00440
Do not twist the sponge material when squeez-
ing it.
9. Check the sponge material and replace it if
damaged.
10. Apply a quality foam air filter oil to the sponge
material.
NOTE:

The sponge material should be wet but not drip-
ping.
11. Pull the sponge material over the air filter ele-
ment frame.
1. Sponge material
2. Air filter element frame
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12. Install the washer onto the air filter element
frame, and then insert the wing bolt into the
hole in the air filter element frame.
CAUTION:

ECB00451
Be sure to install the washer with the bent edge
facing outward as shown.
13. Insert the air filter element into the air filter
case, and then tighten the wing bolt.
14. Install the air filter case cover by hooking the
holders onto the air filter case.
15. Install the seat.
NOTE:

The air filter element should be cleaned every 20–
40 hours. It should be cleaned and lubricated more
often if the ATV is operated in extremely dusty ar-
eas. Each time the air filter element maintenance
is performed, check the air inlet of the air filter case
for obstructions. Check the air filter case rubber
joint to the carburetor fittings and the rubber joint
manifold fittings for an air-tight seal. Tighten all fit-
tings securely to avoid the possibility of unfiltered
air entering the engine.
CAUTION:

ECB00460

Make sure that the air filter element is prop-
erly seated in the air filter case.

Never operate the engine with the air filter el-
ement removed. This will allow unfiltered air
to enter the engine, causing rapid engine
wear and possible engine damage. Addition-
ally, operation without the air filter element
will affect carburetor jetting with subsequent
poor performance and possible engine over-
heating.
1. Washer
1

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7. Start the engine and rev it up approximately
twenty times while momentarily creating ex-
haust system back pressure by blocking the
end of the muffler with a shop towel.
8. Stop the engine and allow the exhaust pipe to
cool.
9. Install the purging bolt and tighten it to the
specified torque.
WARNING

EWB02380
Never run the engine in an enclosed area when
purging the spark arrester, otherwise it could
cause injury to the eyes, burns, carbon monox-
ide poisoning, possibly leading to death, and
start a fire.

Always let the exhaust system cool prior to
touching exhaust components.

Always wear eye protection, and make sure
no one is behind the ATV.

Make sure there are no combustible materi-
als in the area.
EBU23940
Adjusting the carburetor
The carburetor should be checked and, if neces-
sary, adjusted at the intervals specified in the peri-
odic maintenance and lubrication chart. The
carburetor is an important part of the engine and
requires very sophisticated adjustment. Therefore,
most carburetor adjustments should be left to a
Yamaha dealer, who has the necessary profes-
sional knowledge and experience. The adjustment
described in the following section, however, may
be performed by the owner as part of routine main-
1. Purging bolt
2. Gasket
Tightening torque:
Purging bolt:
27 Nm (2.7 m·kgf, 20 ft·lbf)
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tenance.
CAUTION:

ECB00480
The carburetor has been set and extensively
tested at the Yamaha factory. Changing these
settings without sufficient technical knowl-
edge may result in poor performance of or
damage to the engine.
EBU24030
Checking the engine idling speed
A special tester is needed to check the engine
idling speed on this model.
Therefore, take the ATV to a Yamaha dealer to
have the engine idling speed checked and adjust-
ed.
EBU24043
Adjusting the throttle cable free play
The throttle cable free play should be checked
and, if necessary, adjusted at the intervals speci-
fied in the periodic maintenance and lubrication
chart.
The throttle cable free play should measure 2.0–4.0 mm (0.08–0.16 in) at the throttle lever. Period-
ically check the throttle cable free play and, if nec-
essary, adjust it as follows.
NOTE:

The engine idling speed must be checked, and ad-
justed if necessary, before adjusting the throttle ca-
ble free play.
1. Loosen the locknut.
2. To increase the throttle cable free play, turn
the adjusting bolt in direction (a). To decrease
the throttle cable free play, turn the adjusting
bolt in direction (b).
Engine idling speed:
1750–1850 r/min

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3. Tighten the locknut.
EBU24060
Valve clearance
The valve clearance changes with use, resulting in
improper air-fuel mixture and/or engine noise. To
prevent this from occurring, the valve clearance
must be adjusted by a Yamaha dealer at the inter-
vals specified in the periodic maintenance and lu-
brication chart.
EBU24130
Checking the front and rear brake pads
The front and rear brake pads must be checked for
wear at the intervals specified in the periodic main-
tenance and lubrication chart.
EBU27711
Front brake pads
Each brake pad is provided with wear indicator
grooves, which allow you to check the brake pad
wear without having to disassemble the brake. To
check the brake pad wear, check the wear indica-
tor grooves. If a brake pad has worn to the point
that the wear indicator grooves are almost in con-
tact with the disc plate, have a Yamaha dealer re-
place the brake pads as a set.
1. Locknut
2. Throttle cable free play adjusting bolt
3. Throttle lever free play
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(a)(b)

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EBU24880
Lubricating the drive chain
The drive chain must be cleaned and lubricated at
the intervals specified in the periodic maintenance
and lubrication chart, otherwise it will quickly wear
out, especially when riding in dusty or wet areas.
Service the drive chain as follows.
CAUTION:

ECB00560
The drive chain must be lubricated after wash-
ing the ATV or riding in the rain.
1. Clean the drive chain with kerosene and asmall soft brush.
CAUTION:

ECB00570
To prevent damaging the O-rings, do not clean
the drive chain with steam cleaners, high-pres-
sure washers or inappropriate solvents.
2. Wipe the drive chain dry.
3. Thoroughly lubricate the drive chain with a
special O-ring chain lubricant.
CAUTION:

ECB00580
Do not use engine oil or any other lubricants
for the drive chain, as they may contain sub-
stances that could damage the O-rings.
EBU24900
Checking and lubricating the cables
The operation and the condition of all control ca-
bles should be checked before each ride, and the
cables and cable ends should be lubricated if nec-
essary. If a cable is damaged or does not move
smoothly, have a Yamaha dealer check or replace
it.
1. O-rings
1

Recommended lubricant:
Engine oil

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EBU25781
Troubleshooting charts
Starting problems or poor engine performance
Check the fuel level in
the fuel tank.1. Fuel
There is enough fuel.
There is no fuel.
Check the compression.
Supply fuel.
The engine does not start.
Check the compression.
Operate the electric starter.2. Compression
There is compression.
There is no compression.
Check the ignition.
Have a Yamaha dealer
check the ATV.
Remove the spark plug
and check the electrodes.3. Ignition
Wipe off with a dry cloth and correct the
spark plug gap, or replace the spark plug.
Have a Yamaha dealer check the ATV.
The engine does not start.
Have a Yamaha dealer
check the ATV.
The engine does not start.
Check the battery.
Operate the electric starter.4. Battery
The engine turns over
quickly.
The engine turns over
slowly.
The battery is good.Check the battery lead connections,
and charge the battery if necessary.
DryWet
Open the throttle halfway and operate
the electric starter.