2002 YAMAHA YZ85 check engine

3 - 5
INSP
ADJ
EC350000
ENGINE
COOLANT LEVEL INSPECTION
WARNING
Do not remove the radiator cap
1, drain
bolt and hoses when the engine and radia-
tor are hot. Scalding 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 counterclockwise to the detent.
This procedure allows any residual pres-
sure to escape. When the hissing sound
has stopped, press down on the cap while
turning counterclockwise and remove it.
CAUTION:
Hard water or salt water is harmful to the
engine parts. You may use distilled water, if
you can’t get soft water.
5PA30010
1. Place the machine on a level place, and
hold it in an upright position.
2. Remove:
lRadiator cap
3. Check:
lCoolant level
Coolant level a low ® Add coolant.
1Radiator
5PA30020
ENGINE/COOLANT LEVEL INSPECTION

3 - 7
INSP
ADJ
RADIATOR CAP INSPECTION
CAUTION:
lDo not mix more than one type of ethyl-
ene glycol antifreeze containing corro-
sion inhibitors for aluminum engine.
lDo not use water containing impurities or
oil.
7. Install:
lRadiator cap
Start the engine and warm it up for a sev-
eral minutes.
8. Check:
lCoolant level
Coolant level low ® Add coolant. Handling notes of coolant:
The coolant is harmful so it should be han-
dled with special care.
WARNING
lWhen coolant splashes to your eye.
Thoroughly wash your eye with water
and see your doctor.
lWhen coolant splashes to your clothes.
Quickly wash it away with water and
then with soap.
lWhen coolant is swallowed.
Quickly make him vomit and take him
to a doctor.
EC355000
RADIATOR CAP INSPECTION
1. Inspect:
lSeal (radiator cap) 1
lValve and valve seat 2
Crack/damage ® Replace.
Exist fur deposits 3 ® Clean or replace.
5PA30050

3 - 10
INSP
ADJTHROTTLE CABLE ADJUSTMENT/
THROTTLE LUBRICATION
EC35A001
THROTTLE CABLE ADJUSTMENT
1. Check:
lThrottle grip free play a
Out of specification ® Adjust.
Throttle grip free play
a:
3 ~ 5 mm (0.12 ~ 0.20 in)
5PA30110
2. Adjust:
lThrottle grip free play
Throttle grip free play adjustment steps:
lLoosen the locknut 1.
lTurn the adjuster 2 until the specified free
play is obtained.
lTighten the locknut.
NOTE:
Before adjusting the throttle cable free play,
the engine idle speed should be adjusted.
WARNING
After adjusting, turn the handlebar to
right and left and make sure that the
engine idling does not run faster.
5PA30120
THROTTLE LUBRICATION
1. Remove:
lThrottle cable cap 1
5PA30130
2. Apply:
lLithium soap base grease
On the throttle cable end a and tube guide
cable winding portion b.
3. Install:
lThrottle grip cap
5PA30140
T R..1 Nm (0.1 m · kg, 0.7 ft · lb)

3 - 23
INSP
ADJ
DRIVE CHAIN SLACK ADJUSTMENT
5. Install:
lDrive chain 1
lJoint 2
lMaster link clip 3
CAUTION:
Be sure to install the master link clip to the
direction as shown.
aTurning direction5PA30530
6. Lubricate:
lDrive chain
Drive chain lubricant:
SAE 10W-30 motor oil or suit-
able chain lubricants
5PA30540
EC36A060
DRIVE CHAIN SLACK ADJUSTMENT
1. Elevate the rear wheel by placing the suit-
able stand under the engine.
2. Check:
lDrive chain slack
a
In the center between the drive axle and
rear wheel axle.
Out of specification ® Adjust.
NOTE:
Before checking and/or adjusting, rotate the
rear wheel through several revolutions and
check the slack several times to find the tight-
est point. Check and/or adjust chain slack with
rear wheel in this “tight chain” position.
Drive chain slack:
35 ~ 45 mm (1.4 ~ 1.8 in)
5PA30550

3 - 32
INSP
ADJ
2. Inspect:
lBearing free play
Exist play ® Replace.
5PA30710
STEERING HEAD INSPECTION AND
ADJUSTMENT
1. Elevate the front wheel by placing a suit-
able stand under the engine.
2. Check:
lSteering stem
Grasp the bottom of the forks and gently
rock the fork assembly back and forth.
Free play ® Adjust steering head.
3. Check:
lSteering smooth action
Turn the handlebar lock to lock.
Unsmooth action ® Adjust steering ring
nut.
5PA30720
5PA30730
4. Adjust:
lSteering ring nut
Steering ring nut adjustment steps:
lRemove the number plate.
lRemove the handlebar and handlebar
upper bracket.
lLoosen the steering ring nut 1 using the
steering nut wrench 2.
Steering nut wrench:
YU-33975/90890-01403
5PA30740
STEERING HEAD INSPECTION AND ADJUSTMENT

3 - 35
INSP
ADJ
ELECTRICAL/SPARK PLUG INSPECTION
EC370000
ELECTRICAL
EC371001
SPARK PLUG INSPECTION
1. Remove:
lSpark plug
2. Inspect:
lElectrode 1
Wear/damage ® Replace.
lInsulator color 2
Normal condition is a medium to light tan
color.
Distinctly different color ® Check the
engine condition.
NOTE:
When the engine runs for many hours at low
speeds, the spark plug insulator will become
sooty, even if the engine and carburetor are in
good operating condition.
3. Measure:
lPlug gap a
Use a wire gauge or thickness gauge.
Out of specification ® Regap.
4. Clean the plug with a spark plug cleaner if
necessary.
Spark plug gap:
0.5 ~ 0.6 mm (0.020 ~ 0.024 in)
5PA30850
5. Tighten:
lSpark plug
NOTE:
lBefore installing a spark plug, clean the gas-
ket surface and plug surface.
lFinger-tighten a the spark plug before torqu-
ing to specification b.
5PA30860
T R..20 Nm (2.0 m · kg, 1.4 ft · lb)

4 - 14
ENGCARBURETOR AND REED VALVE
9. Install:
lMixing chamber top 1
lScrew (mixing chamber top) 2
To carburetor 3.
NOTE:
lPass the throttle cable in front of the carbure-
tor breather hoses.
lAfter installing, check the throttle grip for
smooth movement.5PA40350
Carburetor installation
1. Install:
lCarburetor 1
NOTE:
Install the projection between the carburetor
joint slots.
5PA40360
2. Tighten:
lScrew (air filter joint) 1
lScrew (carburetor joint) 2
5PA40370
3. Clamp:
lCarburetor breather hose 1
lOverflow hose 2
Refer to “CABLE ROUTING DIAGRAM”
section in the CHAPTER 2.
5PA40380
4. Adjust:
lEngine idling speed
Refer to “ENGINE IDLING SPEED
ADJUSTMENT” section in the CHAPTER 3.

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ENG
NOTE:
When you purchase a cylinder, you cannot
designate its size. Choose the piston that
matches the above chart.
ASSEMBLY AND INSTALLATION
Piston ring and piston
1. Install:
lPiston ring 1
NOTE:
lTake care not to scratch the piston or dam-
age the piston ring.
lAlign the piston ring gap with the pin 2.
lAfter installing the piston ring, check the
smooth movement of it.
5PA40620
2. Install:
lGasket (cylinder) 1
lSmall end bearing 2
lDowel pin 3
NOTE:
lApply the engine oil on the bearing (crank-
shaft and connecting rod) and connecting
rod big end washers.
lInstall the gasket with the seal print side
toward the crankcase.
5PA40630
CYLINDER HEAD, CYLINDER AND PISTON