2001 YAMAHA YZ250LC check oil

6-5
IGNITION SYSTEMELEC
2. Inspect:
9Source coil 1 resistance
Out of specification ÕReplace.
3. Inspect:
9Source coil 2 resistance
Out of specification ÕReplace.
EC628000
CDI UNIT INSPECTION
Check all electrical components. If no fault is
found, replace the CDI unit. Then check the
electrical components again.
Tester (+) leadÕBlack/Red lead 1
Tester (–) lead
ÕBlacklead 2
Source coil 1 Tester selector
resistance position
720~1,080½at
½´ 100
20°C (68°F)
Tester (+) leadÕGreen/Blue lead 1
Tester (–) lead
ÕGreen/White lead 2
Source coil 2 Tester selector
resistance position
44~66½at
½´ 10
20°C (68°F)
5MW-9-30-6 7/6/00 1:36 PM Page 12

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
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6-7
SOLENOID VALVE SYSTEMELEC
EC624000
COUPLERS AND LEADS CONNECTION
INSPECTION
1. Check:
9Couplers and leads connection
Rust/ Dust/ Looseness/Short-circuit Õ
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 Õ
Replace.
EC653002
SOLENOID VALVE COIL INSPECTION
1. Inspect:
9Solenoid valve coil resistance
Out of specification ÕReplace.
Tester (+) leadÕRed lead 1
Tester (–) lead
ÕRed lead 2
22.8~27.8½at
20°C (68°F)Solenoid
resistance
Tester selector
position
½´ 10
Battery (+) leadÕRed lead 1
Battery (–) lead
ÕRed lead 2
5MW-9-30-6 7/6/00 1:37 PM Page 18

6-8
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
5MW-9-30-6 7/6/00 1:37 PM Page 20

6-9
TPS (THROTTLE POSITION SENSOR) SYSTEMELEC
EC624000
COUPLERS AND LEADS CONNECTION
INSPECTION
1. Check:
9Couplers and leads connection
Rust/ Dust/ Looseness/Short-circuit Õ
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 ÕReplace.
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 ÕReplace.
Tester (+) leadÕBluelead 1
Tester (–) lead
ÕBlacklead 2
TPS coil Tester selector
resistance position
4~6k½at
k½´1
20°C (68°F)
Tester (+) leadÕYellowlead 2
Tester (–) lead
ÕBlacklead 3
Tester selector
positionTPS coil variable
resistance
Full closed Full opened
Zero~2k½at 4~6k½at
20°C (68°F) 20°C (68°F)
k½´1
5MW-9-30-6 7/6/00 1:38 PM Page 24

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 tak-
ing 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)
7
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7-2
SETTINGTUN
That is:
9Higher temperature expands the air with its
resultant reduced density.
9Higher humidity reduces the amount of oxygen
in the air by so much of the water vapor in the
same air.
9Lower atmospheric pressure (at a high altitude)
reduces the density of the air.
EC713001
Test run
After warming up the engine equipped with the
standard type carburetor(s) and spark plug(s),
run two or three laps of the circuit and check the
smooth operation of the engine and discoloration
of spark plug(s).
ŒNormal
ºOver burned (too lean)
Oil fouled (too rich)
Discoloration Condition of spark plug
NormalInsulator is dry and
burnt brown.
Over burned
Insulator is whitish.
(too lean)
Oil fouled Insulator is sooty and
(too rich) wet.
A
B
C
5MW-9-30-7 7/6/00 2:16 PM Page 4

7-12
SETTINGTUN
EC71M001
Change of the heat range of spark plugs
Judging from the discoloration of spark plugs, if
they are found improper, it can be corrected by
the following two methods; changing carburetor
settings and changing the heat range of spark
plug.
9In principle, it is advisable to first use spark
plugs of standard heat range, and judging from
the discoloration of spark plugs, adjust carbure-
tor settings.
9If the calibration No. of the main jet must be
changed by ±30, it is advisable to change the
heat range of spark plugs and newly select the
proper main jet.
NOTE:
9When checking the discoloration of spark
plugs, be sure to stop the engine immediately
after a run and check.
9Avoid racing.
9When changing the heat range of spark plugs,
never attempt to change it more than ±1 rank.
9When using spark plugs other than standard,
make sure of the difference in heat range and
find the equivalent to the standard.
9Note that even if the discoloration seems prop-
er, it may slightly vary with the spark plug
maker and oil in use.
Standard spark plug BR8EG/NGK
5MW-9-30-7 7/6/00 2:19 PM Page 28