2006 YAMAHA YZ250LC fuel

4-9
ENGCARBURETOR 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.
1P8-9-31-4A 5/12/05 1:18 PM Page 18

4-18
CYLINDER HEAD, CYLINDER AND PISTONENG
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)
64 Nm (6.4 m•kg, 46 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)
13 Nm (1.3 m•kg, 9.4 ft•lb)
42 Nm (4.2 m•kg, 30 ft•lb)
13 Nm (1.3 m•kg, 9.4 ft•lb)
1P8-9-31-4A 5/12/05 1:19 PM Page 36

4-56
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) 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



7 Nm (0.7 m•kg, 5.1 ft•lb)
5 Nm (0.5 m•kg, 3.6 ft•lb)
56 Nm (5.6 m•kg, 40 ft•lb)
1P8-9-31-4C 5/12/05 1:20 PM Page 14

Extent of removal Order Part name Q’ty Remarks
ENGINE REMOVAL
Preparation for
Hold the machine by placing the
removalsuitable stand under the engine.
Drain the transmission oil. Refer to “TRANSMISSION OIL
REPLACEMENT” section in the
CHAPTER 3.
Seat and fuel tankRefer to “SEAT, FUEL TANK AND
SIDE COVERS” section.
CarburetorRefer 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.
4-60
ENGINE REMOVALENG
EC4M0000
ENGINE REMOVAL
w
Support the machine securely so there is no dan-
ger of it falling over.



26 Nm (2.6 m•kg, 19 ft•lb)
64 Nm (6.4 m•kg, 46 ft•lb)
75 Nm (7.5 m•kg, 54 ft•lb)
5 Nm (0.5 m•kg, 3.6 ft•lb)
34 Nm (3.4 m•kg, 24 ft•lb)
64 Nm (6.4 m•kg, 46 ft•lb)
85 Nm (8.5 m•kg, 61 ft•lb)
åExcept for USA and CDN
4 Nm (0.4 m•kg, 2.9 ft•lb)
1P8-9-31-4C 5/12/05 1:20 PM Page 22

Extent of removal Order Part name Q’ty Remarks
FRONT FORK REMOVAL
Preparation for
Hold the machine by placing the
removalsuitable stand under the engine.
Front wheel Refer to “FRONT WHEEL AND
REAR WHEEL”section.
Front caliper Refer to “FRONT BRAKE AND
REAR BRAKE”section.
Number plate
Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section in the CHAPTER 4.
1 Protector 1
2 Pinch bolt (handle crown) 2 Only loosening.
3 Damper assembly 1
Loosen when disassembling the front fork.
Use special tool. Refer to “REMOVAL POINTS”.
4 Pinch bolt (under bracket) 2 Only loosening.
5 Front fork 1
5-26
CHASFRONT FORK
1
w
Support the machine securely so there is no dan-
ger of it falling over.
Extent of removal:1Front fork removal
7 Nm (0.7 m•kg, 5.1 ft•lb)
7 Nm (0.7 m•kg, 5.1 ft•lb)
7 Nm (0.7 m•kg, 5.1 ft•lb)
20 Nm (2.0 m•kg, 14 ft•lb)
23 Nm (2.3 m•kg, 17 ft•lb)
EC550000
FRONT FORK
1P8-9-31-5B 5/12/05 10:57 AM Page 2

5-50
CHASSTEERING
Extent of removal Order Part name Q’ty Remarks
STEERING REMOVAL
Preparation for
Hold the machine by placing the
removalsuitable stand under the engine.
Number plateRefer to “SEAT, FUEL TANK AND SIDE COVERS”
section in the CHAPTER 4.
Handlebar Refer to “HANDLEBAR” section.
Front fender
1 Steering shaft cap 1
2 Steering shaft nut 1
3 Front fork 2 Refer to “FRONT FORK” section.
4 Handle crown 1
5 Ring nut 1 Use special tool.
Refer to “REMOVAL POINTS”.
6 Under bracket 1
7 Bearing race cover 1
8 Bearing (upper) 1
9 Bearing (lower) 1 Refer to “REMOVAL POINTS”.
10 Bearing race 2 Refer to “REMOVAL POINTS”. Extent of removal:1Under bracket removal 2Bearing removal
2
1
w
Support the machine securely so there is no dan-
ger of it falling over.
EC560000
STEERING
145 Nm (14.5 m•kg, 105 ft•lb)
23 Nm (2.3 m•kg, 17 ft•lb)
9Tighten ring nut.
38 Nm (3.8 m•kg, 27 ft•lb)
9Loosen it one turn.
9Retighten it.
7 Nm (0.7 m•kg, 5.1 ft•lb)
TIGHTENING STEPS:
20 Nm (2.0 m•kg, 14 ft•lb)
4Nm (0.4 m•kg, 2.9 ft•lb)
1P8-9-31-5C 5/12/05 11:28 AM Page 18

5-63
CHASREAR SHOCK ABSORBER
Extent of removal:1Rear shock absorber removal 2Rear shock absorber disassembly
56 Nm (5.6 m•kg, 40 ft•lb)
53 Nm (5.3 m•kg, 38 ft•lb)
32 Nm (3.2 m•kg, 23 ft•lb)
EC580000
REAR SHOCK ABSORBER
29 Nm (2.9 m•kg, 21 ft•lb)
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 in the CHAPTER 4.
SilencerRefer to “EXHAUST PIPE AND
SILENCER” section in the CHAPTER 4.
1 Clamp (air cleaner joint) 1 Loosen the bolt (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 seat 2
9 Spring guide (lower) 1
10 Spring guide (upper) 1
11 Spring (rear shock absorber) 1
12 Bearing 2 Refer to “REMOVAL POINTS”.
2
w
Support the machine securely so there is no dan-
ger of it falling over.
1
1P8-9-31-5D 4/29/05 2:14 PM Page 18

6-2
IGNITION SYSTEMELEC
EC620000
IGNITION SYSTEM
EC621003
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.
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
OKReplace.
Check spark plug cap.No good
OK
No good
Replace.
Replace CDI unit
OK
Check neutral switch
(Except for USA and CDN)
1P8-9-31-6 5/12/05 10:25 AM Page 4