2002 YAMAHA YZ250LC stop start

2-5
MAINTENANCE SPECIFICATIONSSPEC
Part to be tightened Thread size Q’tyT ightening torqueNm m•kg ft•lb
Spark plug M14 ×1.25 1 20 2.0 14
Cylinder head (nut) M 8 ×1.25 6 25 2.5 18
(stud) M 8 ×1.25 6 13 1.3 9.4
Cylinder (nut) M10 ×1.25 4 35 3.5 25
(stud) M10 ×1.25 4 13 1.3 9.4
Power valve :
Holder M 5 ×0.8 2 6 0.6 4.3
Link rod M 5 ×0.8 2 6 0.6 4.3
Push rod M 5 ×0.8 1 5 0.5 3.6
Thrust plate M 5 ×0.8 1 6 0.6 4.3
Side holder M 5 ×0.8 4 4 0.4 2.9
Link lever M 4 ×0.7 1 4 0.4 2.9
Pulley M 4 ×0.7 2 4 0.4 2.9
Cover M 5 ×0.8 4 4 0.4 2.9
Governor fork M 4 ×0.7 2 5 0.5 3.6
Housing M 5 ×0.8 4 5 0.5 3.6
Impeller M 8 ×1.25 1 14 1.4 10
Water pump housing cover M 6 ×1.0 4 10 1.0 7.2
Coolant drain bolt M 6 ×1.0 1 10 1.0 7.2
Radiator M 6 ×1.0 6 10 1.0 7.2
Radiator panel M 6 ×1.0 2 10 1.0 7.2
Radiator hose clamp M 6 ×1.0 8 1 0.1 0.7
Air filter element M 6 ×1.0 1 2 0.2 1.4
Carburetor joint M 6 ×1.0 5 10 1.0 7.2
Air filter case M 6 ×1.0 4 8 0.8 5.8
Air filter guide clamp M 5 ×0.8 1 1 0.1 0.7
Reed valve M 3 ×0.5 4 1 0.1 0.7
Exhaust pipe (front) M 6 ×1.0 1 14 1.4 10
Exhaust pipe (rear) M 6 ×1.0 1 12 1.2 8.7
Exhaust pipe stay (front) M 8 ×1.25 1 25 2.5 18
Exhaust pipe stay (rear) M 6 ×1.0 1 12 1.2 8.7
Silencer (front) M 6 ×1.0 1 12 1.2 8.7
Silencer (rear) M 6 ×1.0 1 7 0.7 5.1
Fiber (silencer) M 6 ×1.0 2 10 1.0 7.2
Crankcase M 6 ×1.0 11 14 1.4 10
Crankcase cover (left) M 6 ×1.0 5 8 0.8 5.8
Chain cover M 6 ×1.0 2 8 0.8 5.8
Crankcase cover (right) M 6 ×1.0 9 10 1.0 7.2
Bearing plate cover (drive axle left) M 6 ×1.0 2 10 1.0 7.2
Bearing plate cover (main axle right) M 6 ×1.0 2 10 1.0 7.2
Holder M 6 ×1.0 2 10 1.0 7.2
Oil drain bolt M12 ×1.5 1 20 2.0 14
Oil check bolt M 6 ×1.0 1 10 1.0 7.2
Kick starter M 8 ×1.25 1 30 3.0 22
Ratchet wheel stopper M 6 ×1.0 2 10 1.0 7.2
Clutch cover M 6 ×1.0 6 10 1.0 7.2
5NX-9-30-2 6/7/01 1:57 PM Page 6

INSP
ADJ
3-15
IDLE SPEED ADJUSTMENT/MUFFLER INSPECTION/
SILENCER FIBER REPLACEMENT
EC35M001
IDLE SPEED ADJUSTMENT
1. Start the engine and thoroughly warm it up.
2. Adjust:
9Idle speed
EC35P030
MUFFLER INSPECTION
1. Inspect:
9O-ring 1
Damage Replace.
NOTE:
Install the O-rings with their depressed afacing
outward.
EC35R050
SILENCER FIBER REPLACEMENT
1. Remove:
9Side cover (right)
9Bolt (silencer) 1
9Silencer 2
9Bolt (fiber) 3 Adjustment steps:
Turn the throttle stop screw 1until the
engine runs at the lowest possible speed.
To increase idle speed Turn the throttle
stop screw 1 1
in.
To decrease idle speed Turn the throttle
stop screw 1 1
out.
5NX-9-30-3A 6/5/01 3:59 PM Page 38

4-8
CARBURETOR AND REED VALVEENG
EC468000
CARBURETOR DISASSEMBLY
Extent of removal Order Part name Q’ty Remarks
CARBURETOR DISASSEMBLY
1Mixing chamber top 1
2Throttle valve 1 Refer to “REMOVAL POINTS”.
3Needle holder 1
4Jet needle 1
5Float chamber 1
6Float pin 1
7Float 1
8Needle valve 1
9Main jet 1
0Pilot jet 1
qStarter plunger 1
wThrottle stop screw 1
ePilot air screw 1 Refer to “REMOVAL POINTS”.
rPower jet 1
tSolenoid valve 1
Extent of removal:1Carburetor disassembly
1
5NX-9-30-4A 6/5/01 4:12 PM Page 16

3. Install:
9Pilot air screw 1
9Throttle stop screw 2
4. Install:
9Starter plunger 1
4-14
ENGCARBURETOR AND REED VALVE
Pilot air screw:
1 turn out
*1-3/8 turns out
(for reference only)
Note the following installation points:
9Turn in the pilot air screw until it is lightly
seated.
9Turn out the pilot air screw by the number
of turns recorded before removing.
5. Install:
9Pilot jet 1
9Main jet 2
2. Install:
9O-ring 1
9Solenoid valve 2
9Clamp 3
9Screw (clamp) 4
To carburetor 5.
cC
9
Before installing the solenoid valve, blow
air on the solenoid valve and its installing
location on the carburetor in order to
remove any foreign particles such as chips
etc.
9Apply the engine oil on the solenoid valve
thread.
*For EUROPE
5NX-9-30-4A 6/5/01 4:12 PM Page 28

4-66
CRANKCASE AND CRANKSHAFTENG
NOTE:
9Make appropriate bolts 3as shown available
by yourself and attach the tool with them.
9Fully tighten the tool holding bolts, but make
sure the tool body is parallel with the case. If
necessary, one screw may be backed out
slightly to level tool body.
9As pressure is applied, alternately tap on the
front engine mounting boss and transmission
shafts.
cC
Use soft hammer to tap on the case half.
Tap only on reinforced portions of case. Do
not tap on gasket mating surface. Work
slowly and carefully. Make sure the case
halves separate evenly. If one end “hangs
up”, take pressure off the push screw,
realign, and start over. If the cases do not
separate, check for a remaining case
screw or fitting. Do not force.
EC4N3000
REMOVAL POINTS
EC4N3100
Segment
1. Remove:
9Bolt (segment) 1
9Segment 2
NOTE:
Turn the segment counterclockwise until it stops
and loosen the bolt.
EC4N3212
Crankcase
1. Remove:
9Crankcase (right) 1
Use the crankcase separating tool 2.
Crankcase separating tool:
YU-1135-A/90890-01135
5NX-9-30-4C 6/5/01 4:25 PM Page 34

6-3
IGNITION SYSTEMELEC
EC622001
SPARK GAP TEST
1. Disconnect the spark plug cap from spark
plug.
2. Connect the dynamic spark tester 1(igni-
tion checker 2) as shown.
9Spark plug cap 3
9Spark plug 4
AFor USA and CDN
BExcept for USA and CDN
3. Kick the kick starter.
4. Check the ignition spark gap.
5. Start engine, and increase spark gap until
misfire occurs. (for USA and CDN only)
EC624000
COUPLERS AND LEADS CONNECTION
INSPECTION
1. Check:
9Couplers and leads connection
Rust/ Dust/ Looseness/Short-circuit 
Repair or replace.
EC625002
“ENGINE STOP” BUTTON INSPECTION
1. Inspect:
9“ENGINE STOP” button conduct
Not continuous while being pushed Replace.
Continuous while being freed Replace.
Minimum spark gap:
6.0 mm (0.24 in)
Tester (+) leadBlack/White lead 1
Tester (–) lead
Black lead 2
B/W B
12
PUSH IN
FREE
Tester selec-
tor position
Ω× 1
å å
B
5NX-9-30-6 6/5/01 4:44 PM Page 8

6-12
TPS (THROTTLE POSITION SENSOR) SYSTEMELEC
10. Put the aligning marks aon the TPS and
carburetor.
11. Stop the engine.
12. Remove:
9Carburetor
Refer to “CARBURETOR AND REED
VALVE” section in the CHAPTER 4.
13. Tighten:
9Screw (TPS) 1
NOTE:
Tighten the screws (TPS) using the T20 bit (tam-
per resistant fastener type) by aligning the
marks athat were put before removal.
14. Install:
9Carburetor
Refer to “CARBURETOR AND REED
VALVE” section in the CHAPTER 4.
8. Start the engine.
9. Adjust:
9TPS output voltage
Adjustment steps:
Adjust the installation angle of the TPS
1to obtain the specified output volt-
age.
TPS output Tester selector
voltage position
0.5~0.7V DCV-20
5NX-9-30-6 6/5/01 4:44 PM Page 30