2001 YAMAHA YZ250LC fuel

ENG
4-9
CARBURETOR AND REED VALVE
EC466020
HANDLING NOTE
cC
Do not loosen the screws {TPS (throttle
position sensor)} except when changing
the TPS (throttle position sensor) due to
failure because it will cause a drop in
engine performance.
EC463000
REMOVAL POINTS
EC463110
Throttle valve
1. Remove:
9Throttle valve 1
9Ring 2
9Spring (throttle valve) 3
9Mixing chamber top 4
9Throttle cable 5
NOTE:
While compressing the spring (throttle valve),
disconnect the throttle cable.
EC463401
Pilot air screw
1. Remove:
9Pilot air screw 1
NOTE:
To optimize the fuel flow at a smaller throttle
opening, each machine’s pilot air screw has
been individually set at the factory. Before
removing the pilot air screw, turn it in fully and
count the number of turns. Record this number
as the factory-set number of turns out.
5MW-9-30-4A 7/3/00 5:03 PM Page 18

ENG
4-17
CYLINDER HEAD, CYLINDER AND PISTON
EC470000
CYLINDER HEAD, CYLINDER AND PISTONEC478000
CYLINDER HEAD AND CYLINDER
Extent of removal Order Part name Q’ty Remarks
CYLINDER HEAD AND
CYLINDER REMOVAL
Preparation for Seat and fuel tank Refer to “SEAT, FUEL TANK AND
removal SIDE COVERS” section.
Exhaust pipe and silencer Refer to ”EXHAUST PIPE AND
SILENCER” section.
Radiator hose 1 Disconnect at cylinder head side.
Carburetor Refer to “CARBURETOR AND REED
VALVE” section.
1 Spark plug 1
2 Engine bracket 2
3 Nut (cylinder head) 6
Loosen each nut 1/4 turn, and remove
them after all nuts are loosened.
4 Cylinder head 1
5 Power valve housing 1
6 Push rod 1 Refer to “REMOVAL POINTS”.
7 Nut (cylinder) 4
8 Cylinder 1
Extent of removal:1Cylinder head removal2Cylinder removal
1
2
34 Nm (3.4 m•kg, 24 ft•lb)
69 Nm (6.9 m•kg, 50 ft•lb)
20 Nm (2.0 m•kg, 14 ft•lb)
5 Nm (0.5 m•kg, 3.6 ft•lb)
5 Nm (0.5 m•kg, 3.6 ft•lb)
25 Nm (2.5 m•kg, 18 ft•lb)
10 Nm (1.0 m•kg, 7.2 ft•lb)
35 Nm (3.5 m•kg, 25 ft•lb)
10 Nm (1.0 m•kg, 7.2 ft•lb)
5MW-9-30-4A 7/3/00 5:28 PM Page 34

4-55
CDI MAGNETOENG
Extent of removal Order Part name Q’ty Remarks
CDI MAGNETO REMOVAL
Preparation for Seat and fuel tank Refer to “SEAT, FUEL TANK AND
removal SIDE COVERS” section.
Bolt [radiator (left)] Refer to “RADIATOR” section.
Disconnect the CDI magneto lead.
1 Crankcase cover (left) 1
2 Nut (rotor) 1 Use special tool.
3 Rotor 1 Refer to “REMOVAL POINTS”.
4 Stator 1
5 Woodruff key 1
EC4L0000
CDI MAGNETO
1
Extent of removal:1CDI magneto removal
ü
ý
þ
8 Nm (0.8 m•kg, 5.8 ft•lb)
8 Nm (0.8 m•kg, 5.8 ft•lb)
41 Nm (4.1 m•kg, 30 ft•lb)
5MW-9-30-4C 7/3/00 7:44 PM Page 14

4-59
ENGINE REMOVALENG
Extent of removal Order Part name Q’ty Remarks
ENGINE REMOVAL
Preparation for
Hold the machine by placing the
removalsuitable stand under the engine.
Seat and fuel tankRefer to “SEAT, FUEL TANK AND
SIDE COVERS” section.
Carburetor and carburetor jointRefer to “CARBURETOR AND REED
VALVE” section.
Exhaust pipe and silencer Refer to “EXHAUST PIPE AND
Exhaust pipe stay (rear) SILENCER” section.
Clutch cable Disconnect at engine side.
Radiator Refer to “RADIATOR” section.
Spark plug
Disconnect the CDI magneto lead.
EC4M0000
ENGINE REMOVAL
w
Support the machine securely so there is no dan-
ger of it falling over.
ü
ý
þ
26 Nm (2.6 m•kg, 19 ft•lb)
69 Nm (6.9 m•kg, 50 ft•lb)
34 Nm (3.4 m•kg, 24 ft•lb)
69 Nm (6.9 m•kg, 50 ft•lb)
75 Nm (7.5 m•kg, 54 ft•lb)
8 Nm (0.8 m•kg, 5.8 ft•lb)
85 Nm (8.5 m•kg, 61 ft•lb)
5MW-9-30-4C 7/3/00 7:47 PM Page 22

5-46
CHASHANDLEBAR
14. Clamp the clamp portion aof the number
plate to the handlebar.
15. Insert the end of the fuel breather hose 1
into the hole of the number plate.
5MW-9-30-5C 7/6/00 10:44 AM Page 14

5-59
CHASREAR SHOCK ABSORBER
EC580000
REAR SHOCK ABSORBER
Extent of removal Order Part name Q’ty Remarks
REAR SHOCK ABSORBER
REMOVAL
Preparation forHold the machine by placing the
removalsuitable stand under the engine.
SeatRefer to “SEAT, FUEL TANK AND
SIDE COVERS” section.
SilencerRefer to “EXHAUST PIPE AND
SILENCER” section.
1 Clamp (air cleaner joint) 1 Loosen the screw (air cleaner joint).
2 Rear 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
7 Adjuster 1
8 Spring guide (lower) 1
9 Spring guide (upper) 1
10 Spring (rear shock absorber) 1
11 Bearing 2 Refer to “REMOVAL POINTS”.
2
w
Support the machine securely so there is no dan-
ger of it falling over.
Extent of removal:1Rear shock absorber removal 2Rear shock absorber disassembly
1
56 Nm (5.6 m•kg, 40 ft•lb)
53 Nm (5.3 m•kg, 38 ft•lb)
29 Nm (2.9 m•kg, 21 ft•lb)
5MW-9-30-5D 7/6/00 11:30 AM Page 16

6-2
IGNITION SYSTEMELEC
EC620000
IGNITION SYSTEM
EC621002
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.
*Clean or replace
spark plug.
Primary coil
Secondary coil
Repair or replace.
Spark
Check entire ignition
system for connection.
Spark gap test
No good
No good
No good
No good
No good
No good No Spark
Check “ENGINE STOP”
button.
Pick-up coil
Source coil
Check ignition coil.
Check CDI magneto.
Replace CDI unit.
Replace.
Replace.
Replace.
Replace.
Replace.
*marked: Only when the ignition checker is used.
NOTE:
9Remove the following parts before inspection.
1) Seat
2) Fuel tank
9Use the following special tools in this inspection.
Dynamic spark tester:
YM-34487
Ignition checker:
90890-06754Pocket tester:
YU-3112-C/90890-03112
OK
OK
OK
OK
5MW-9-30-6 7/6/00 1:34 PM Page 4

6-6
SOLENOID VALVE SYSTEMELEC
Check solenoid
valve operation.
Solenoid valve
coil
No good
No good
Check each couplers and
wire connection.
Check solenoid valve.
Repair or replace.
Replace.
Replace.
OK
OK
OKSource coil
No goodReplace.* Check CDI magneto.
Replace CDI unit.
No good
EC650001
SOLENOID VALVE SYSTEM
EC651032
INSPECTION STEPS
If the solenoid valve will not operate, use the following inspection steps.
* marked: Refer to "IGNITION SYSTEM" section.
NOTE:
9Remove the following parts before inspection.
1) Seat
2) Fuel tank
9Use l2V battery in this inspection.
9Use the following special tools in this inspection.
Pocket tester:
YU-3112-C/90890-03112
5MW-9-30-6 7/6/00 1:36 PM Page 14