2006 YAMAHA YZ250LC engine

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.
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6-12
TPS (THROTTLE POSITION SENSOR) SYSTEMELEC
4. Install:
9TPS 1
9Screw (TPS) 2
NOTE:
9Align the slot ain the TPS with the projection
bon the carburetor while the lever 3is held
down.
9Temporarily tighten the screws (TPS).
5. Install:
9Mixing chamber top
9Carburetor
Refer to “CARBURETOR AND REED
VALVE” section in the CHAPTER 4.
6. Adjust:
9Idle speed for TPS adjustment
Idle speed for TPS adjustment:
1,700~1,900 rpm
Adjustment steps:
9Set the inductive tachometer (engine
tachometer) to the high tension cord.
9Turn the throttle stop screw 1until the
specified idle speed.
Refer to “IDLE SPEED ADJUSTMENT” sec-
tion in the CHAPTER 3.
7. Insert the thin electric conductors 2(lead
wire) into the TPS coupler 1, as shown,
and connect the tester to them.
cC
9Do not insert the electric conductors
more than required because it may reduce
the waterproof function of the coupler.
9Make sure that a short-circuit does not
develop between the terminals because it
may cause damage to electrical compo-
nents.
Tester (+) leadYellowlead 3
Tester (–) lead
Blacklead 4
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6-13
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
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6-14
TPS (THROTTLE POSITION SENSOR) SYSTEMELEC
EC694000
TPS INPUT VOLTAGE INSPECTION
1. Disconnect the TPS coupler.
2. Start the engine.
3. Inspect:
9TPS input voltage
Out of specification Replace the CDI
unit.
Tester (+) leadBluelead 1
Tester (–) lead
Black/Bluelead 2
TPS input Tester selector
voltage position
4~6V DCV-20
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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)
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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).
åNormal
∫Over burned (too lean)
çOil 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
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7-3
SETTINGTUN
EC714032
Effects of setting parts in relation to throt-
tle valve opening
NOTE:
The power jet closes at 8,500 rpm of the engine,
after which only the main jet dominates.
1Throttle valve opening
2Full-open
3Full-closed
EC715002
Main jet adjustment
The richness of air-fuel mixture with 3/4~4/4
throttle can be set by changing the main jet 1.
*For EUROPE
1. Spark plug is too hot.
Select a main jet having higher calibrating
No. than standard. (To be enriched)
2. Spark plug is wet.
Select a main jet having lower calibrating No.
than standard. (To be leaned out)
Standard main jet#178
*#180
EC71V000
Power jet adjustment
The richness of air-fuel mixture under 8,500 rpm
to the extent of 1/2 to full opened throttle can be
set by changing the power jet 1. A larger size jet
results in a richer mixture, and a smaller size in a
leaner mixture.
Standard power jet #50
Setting partThrottle valve openingFull-closed 1/4 1/2 3/4 Full-open
Pilot jet
Pilot air screw
Diameter of
straight portion
Clip position
Throttle valve
Power jet
Main jet
Jet needle
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7-4
SETTINGTUN
EC71R010
Pilot jet adjustment
The richness of air - fuel mixture with the throttle
fully closed to 1/2 open can be set by turning the
pilot jet 1.
It is changed when adjustment cannot be made
by the pilot air screw alone.
EC718001
Jet needle groove position adjustment
Should the engine be hard to run smoothly at
intermediate speeds, the jet needle 1must be
adjusted. If the mixture is too rich or too lean at
intermediate speed operation, irregular engine
operation and poor acceleration will result.
Whether or not the richness of the mixture is
proper is hard to be determined by means of the
spark plug and therefore, it should be judged
from your feeling of actual engine operation.
*For EUROPE
Standard pilot jet#50
*#52
EC716001
Pilot air screw adjustment
The richness of air-fuel mixture with full closed to
1/8 throttle can be set by turning the pilot air
screw 1.
Turning in the pilot air screw will enrich the mix-
ture at low speeds, and turning out it will lean out
the mixture.
*For EUROPE
**For AUS, NZ and ZA
*For EUROPE
1 turn out
Standard pilot air *2-1/4 turns out
screw position **1-1/4 turns out
(for reference only)
Standard clip positionNo.2 groove
*No 3 groove
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