2002 YAMAHA YZ85 fuel

4 - 15
ENGCYLINDER HEAD, CYLINDER AND PISTON
EC470000
CYLINDER HEAD, CYLINDER AND PISTON
EC478000
CYLINDER HEAD AND CYLINDER
5PA40390
Extent of removal:
1 Cylinder head removal
2 Cylinder removal
Extent of removal Order Part name Q’ty Remarks
CYLINDER HEAD AND CYLIN-
DER REMOVAL
Preparation for removal Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Exhaust pipe and silencer Refer to “EXHAUST PIPE AND
SILENCER” section.
Radiator hose 1 Disconnect at cylinder head side.
Radiator hose 2 Disconnect at radiator side.
1 Spark plug 1
2 Nut (cylinder head) 4 Loosen each nut 1/4 turn, and remove
them after all nuts are loosened.
3 Cylinder head 1
4 Nut (cylinder) 4
5 Cylinder 1
1
2

4 - 45
ENG
EC4L0000
CDI MAGNETO
5PA41380
Extent of removal:
1 CDI magneto removal
Extent of removal Order Part name Q’ty Remarks
CDI MAGNETO REMOVAL
Preparation for removal Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Disconnect the CDI magneto lead.
1 Left crankcase cover 1
2 Nut (rotor) 1 Use special tool.
Refer to “REMOVAL POINTS”.
3 Rotor 1
4 Stator 1
5Woodruff key
1
1
CDI MAGNETO

4 - 49
ENG
EC4M0000
ENGINE REMOVAL
5PA41490
Extent of removal Order Part name Q’ty Remarks
ENGINE REMOVAL
Preparation for removal Hold the machine by placing the
suitable stand under the frame.
WARNING
Support the machine securely so there is no
danger of it falling over.
Drain the coolant. Refer to “COOLANT REPLACEMENT”
section in the CHAPTER 3.
Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Carburetor Refer to “CARBURETOR AND REED
VALVE” section.
Exhaust pipe and silencer Refer to “EXHAUST PIPE AND
SILENCER” section.
Clutch cable Disconnect at engine side.
Radiator hose 1 Disconnect at cylinder head side.
Radiator hose 2 Disconnect at water pump side.
Spark plug cap
Disconnect the CDI magneto
lead.
ENGINE REMOVAL

5 - 45
CHAS
7. Install:
lEngine stop switch 1
lClutch lever holder 2
lBolts (clutch lever holder) 3
lClamp 4
NOTE:
The engine stop switch and clutch lever holder
should be installed according to the dimen-
sions shown.
5PA51420
T R..4 Nm (0.4 m · kg, 2.9 ft · lb)
5PA51430
8. Install:
lClutch cable 1
NOTE:
Apply the lithium soap base grease on the
clutch cable end.
5PA51440
9. Adjust:
lClutch lever free play
Refer to “CLUTCH ADJUSTMENT” section
in the CHAPTER 3.
10. Clamp the clamp portion a of the number
plate to the handlebar.
11. Insert the end of the fuel tank breather
hose 1 into the hole of the steering stem.
5PA51450
HANDLEBAR

5 - 59
CHASREAR SHOCK ABSORBER
EC580000
REAR SHOCK ABSORBER
5PA51870
Extent of removal:
1 Rear shock absorber removal
2 Rear shock absorber disassembly
Extent of removal Order Part name Q’ty Remarks
Preparation for removalREAR SHOCK ABSORBER
REMOVAL
Hold the machine by placing the
suitable stand under the engine.
WARNING
Support the machine securely so there is no
danger of it falling over.
Seat Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section in the CHAPTER 4.
Silencer Refer to “EXHAUST PIPE AND
SILENCER” section in the CHAPTER 4.
1 Clamp (air cleaner joint) 1 Only loosening.
2Rear frame 1
3 Bolt (rear shock absorber-relay
arm)1 Hold the swingarm.
4 Bolt (rear shock absorber-frame) 1
5 Rear shock absorber 1
6 Locknut 1 Only loosening.
7 Adjuster 1 Only loosening.
8 Spring guide 1
9 Spring (rear shock absorber) 1
1
2

6 - 2
–+ELECIGNITION SYSTEM
EC620000
IGNITION SYSTEM
INSPECTION STEPS
Use the following steps for checking the possibility of the malfunctioning engine being attributable to
ignition system failure and for checking the spark plug which will not spark.
*marked: Only when the ignition checker is used.
NOTE:
lRemove the following parts before inspection.
1) Seat
2) Fuel tank
lUse the following special tools in this inspection.
Dynamic spark tester:
YM-34487
Ignition checker:
90890-06754Pocket tester:
YU-3112-C/90890-03112
Spark gap test*Clean or replace
spark plug.
Check entire ignition
system for connection.Repair or replace.
Check engine stop switch. Replace.
Check ignition coil. Primary coil Replace.
Secondary coil Replace.
Check CDI magneto. Pickup coil Replace.
Charging coil Replace.
Replace CDI unit.
No spark
OK
OK
OK
OK
Spark
No good
No good
No good
No good
No good
No good

7 - 1
TUN
EC700000
TUNING
EC710000
ENGINE
Carburetor setting
lThe role of fuel is to cool the engine, and in
the case of a 2-stroke engine, to lubricate the
engine in addition to power generation.
Accordingly, if a mixture of air and fuel is too
lean, abnormal combustion will occur, and
engine seizure may result. If the mixture is
too rich, spark plugs will get wet with oil, thus
making it impossible to bring the engine into
full play or if the worst comes to the worst,
the engine may stall.
lThe richness of the air-fuel mixture required
for the engine will vary with atmospheric con-
ditions of the day and therefore, the settings
of the carburetor must be properly suited to
the atmospheric conditions (air pressure,
humidity and temperature).
lFinally, the rider himself must make a test
run and check his machine for conditions
(pick-up of engine speed, road surface con-
ditions) and for the discoloration of the spark
plug(s).
After taking these into consideration, he must
select the best possible carburetor settings.
* It is advisable to make a note of settings,
atmospheric conditions, road surface condi-
tion, lap-time, etc. so that the memorandum
can be used as a reference useful for future.
Atmospheric conditions and carburetor
settings
The air density (i.e., concentration of oxygen
in the air) determines the richness or lean-
ness of the air/fuel mixture. Therefore, refer
to the above table for mixture settings.
Air temp. HumidityAir
pressure
(altitude)Mixture Setting
High High Low (high) Richer Leaner
Low Low High (low) Leaner Richer
SETTING






7

7 - 3
TUNSETTING
Effects of the setting parts on the throttle
valve opening
1Throttle valve opening
2Full-open
3Full-closed
Setting partThrottle valve openingFull-closed1/4 1/2 3/4 Full-open
Pilot jet
Pilot air screw
Jet needle
Diameter of
straight por-
tion
Clip position
Main jet
5PA70040
Main jet adjustment
The richness of air-fuel mixture with 3/4 ~ 4/4
throttle can be set by changing the main jet 1
.
1. Spark plug is too hot.
Select a main jet having higher calibrating
No. than standard. (To be enriched)
2. Spark plug is wet.
Select a main jet having lower calibrating
No. than standard. (To be leaned out)Standard main jet #138
5PA70050
Pilot air screw adjustment
The richness of the air-fuel mixture with the
throttle fully closed to 1/4 open can be set by
turning the pilot air screw 1
.
Turning in the pilot air screw will make the mix-
ture lean at low speeds, and turning it out will
enrich it.
Standard pilot air
screw position2 turns out
(example)
5PA70060