2005 YAMAHA YZ250LC oil

6-5
IGNITION SYSTEMELEC
2. Inspect:
9Source coil 1 resistance
Out of specification Replace.
Tester (+) leadBlack/Red lead 1
Tester (–) lead
Blacklead 2
Source coil 1 Tester selector
resistance position
720~1,080Ωat
Ω× 100
20°C (68°F)
EC62B000
SPARK PLUG CAP INSPECTION
1.Inspect:
9Spark plug cap
Loose connection Tighten.
Deteriorated/Damaged Replace.
9Spark plug cap resistance
Out of specification Replace.
Tester (+) leadSpark plug lead terminal1
Tester (–) lead
Spark plug terminal2
Spark plug cap Tester selector
resistance position
4~6kΩat
kΩ× 1
20°C (68°F)
EC627011
CDI MAGNETO INSPECTION
1. Inspect:
9Pick-up coil resistance
Out of specification Replace.
Tester (+) leadWhite/Red lead 1
Tester (–) lead
White/Blue lead 2
Pick–up coil Tester selector
resistance position
248~372Ωat
Ω× 100
20°C (68°F)
1P8-9-30-6 21/5/04 11:42 AM Page 12

6-6
IGNITION SYSTEMELEC
3. Inspect:
9Source coil 2 resistance
Out of specification Replace.
EC628000
CDI UNIT INSPECTION
Check all electrical components. If no fault is
found, replace the CDI unit. Then check the
electrical components again.
Tester (+) leadGreen/Blue lead 1
Tester (–) lead
Green/White lead 2
Source coil 2 Tester selector
resistance position
44~66Ωat
Ω× 10
20°C (68°F)
1P8-9-30-6 21/5/04 11:43 AM Page 14

6-7
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
1P8-9-30-6 21/5/04 11:43 AM Page 16

6-8
SOLENOID VALVE SYSTEMELEC
EC624000
COUPLERS AND LEADS CONNECTION
INSPECTION
1. Check:
9Couplers and leads connection
Rust/ Dust/ Looseness/Short-circuit 
Repair or replace.
EC652040
SOLENOID VALVE OPERATION
1. Disconnect the solenoid valve coupler.
2. Connect 12V battery to the solenoid valve
coupler.
3. Inspectt:
9Solenoid valve
1
No click when connecting the battery 
Replace.
EC653002
SOLENOID VALVE COIL INSPECTION
1. Inspect:
9Solenoid valve coil resistance
Out of specification Replace.
R
1
2
12R
R
1
2
12R
Tester (+) leadRed lead 1
Tester (–) lead
Red lead 2
22.8~27.8Ωat
20°C (68°F) Solenoid
resistance
Tester selector
position
Ω× 10
Battery (+) leadRed lead 1
Battery (–) lead
Red lead 2
1P8-9-30-6 21/5/04 11:43 AM Page 20

6-9
TPS (THROTTLE POSITION SENSOR) SYSTEMELEC
Check entire ignition
system for connection.Repair or replace.
OK
OKTPS coil
No goodReplace.Check TPS.
OKSource coil
No goodReplace.*Check CDI magneto.
TPS input
voltageNo goodReplace.Check CDI unit.
No good
EC690000
TPS (THROTTLE POSITION SENSOR) SYSTEM
EC691001
INSPECTION STEPS
If the TPS 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 the following special tools in this inspection.
Inductive tachometer:
YU-8036-B
Engine tachometer:
90890-03113Pocket tester:
YU-3112-C/90890-03112
1P8-9-30-6 21/5/04 11:43 AM Page 22

6-10
TPS (THROTTLE POSITION SENSOR) SYSTEMELEC
L
Y
B1
21
2
EC624000
COUPLERS AND LEADS CONNECTION
INSPECTION
1. Check:
9Couplers and leads connection
Rust/ Dust/ Looseness/Short-circuit 
Repair or replace.
EC692000
TPS COIL INSPECTION
1. Remove:
9Carburetor
9Mixing chamber top
Refer to “CARBURETOR AND REED
VALVE” section in the CHAPTER 4.
2. Inspect:
9TPS coil resistance
Out of specification Replace.
Tester (+) leadBluelead 1
Tester (–) lead
Blacklead 2
TPS coil Tester selector
resistance position
4~6kΩat
kΩ×1
20°C (68°F)
EC69A000
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.
1P8-9-30-6 21/5/04 11:43 AM Page 26

6-11
TPS (THROTTLE POSITION SENSOR) SYSTEMELEC
32
1 2
3L
Y
B
3. Inspect:
9TPS coil variable resistance
Check that the resistance in increased as
the lever 1is moved from the full close
position to the full open position.
Out of specification Replace.
Tester (+) leadYellowlead 2
Tester (–) lead
Blacklead 3
Tester selector
position
Full closed Full opened
Zero~2kΩat 4~6kΩat
20°C (68°F) 20°C (68°F)
kΩ×1
EC693001
TPS REPLACEMENT AND ADJUSTMENT
1. Remove:
9Carburetor
9Mixing chamber top
Refer to “CARBURETOR AND REED
VALVE” section in the CHAPTER 4.
2. Remove:
9Screw (TPS) 1
9TPS 2
NOTE:
Loosen the screws using the T25 bit.
3. Replace:
9TPS
TPS coil variable
resistance
1P8-9-30-6 21/5/04 11:43 AM Page 28

7-1
SETTINGTUN
EC700000
TUNINGEC710000
ENGINEEC711001
Carburetor setting
9The 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. Accord-
ingly, 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.
9The richness of the air-fuel mixture required for
the engine will vary with atmospheric conditions
of the day and therefore, the settings of the car-
buretor must be properly suited to the atmos-
pheric conditions (air pressure, humidity and
temperature).
9Finally, the rider himself must make a test-run
and check his machine for conditions (pick-up
of engine speed, road surface conditions) 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 condition,
lap-time, etc. so that the memorandum can be
used as a reference useful for future.
EC712000
Atmospheric conditions and carburetor
setting
The reason for the above tendency is that the
richness or leanness of a fuel mixture depends
on the density of the air (i.e. the concentration of
oxygen in it).
Air
Air temp. Humidity pressure Mixture Setting
(altitude)
High HighLow
Richer Leaner
(high)
Low LowHigh
Leaner Richer
(low)
1P8-9-30-7 20/5/04 2:10 PM Page 2