2008 YAMAHA WR 250F check engine

7-16
THROTTLE POSITION SENSOR SYSTEM
HANDLING NOTE
Do not loosen the screw (throttle
position sensor) "1" except when
changing the throttle position sen-
sor due to failure because it will
cause a drop in engine perfor-
mance.
CHECKING THE COUPLERS AND
LEADS CONNECTION
1. Check: • Couplers and leads connectionRust/dust/looseness/short-circuit
→ Repair or replace.
CHECKING THE THROTTLE
POSITION SENSOR COIL
1. Inspect: • Throttle position sensor coil resis-tance
Out of specification →Replace.
2. Loosen: • Throttle stop screw "1"
Turn out the throttle stop screw until
the throttle shaft is in the full close po-
sition.
3. Inspect:• Throttle position sensor coil vari-able resistance
Check that the resistance in in-
creased as the throttle grip is
moved from the full close position
to the full open position.
Out of specification →Replace.
CHANGING AND ADJUSTING THE
THROTTLE POSI TION SENSOR
1. Remove: • Throttle position sensor coupler
• Carburetor
2. Remove: • Screw (throttle position sensor) "1"
• Throttle position sensor "2"
Loosen the screw (throttle position
sensor) using the T25 bit.
3. Replace: • Throttle position sensor
4. Install: • Throttle position sensor "1"
• Screw (throttle position sensor) "2"
• Align the slot "a" in the throttle posi-tion sensor with the projection "b"
on the carburetor.
• Temporarily tighten the screw (throttle position sensor).
5. Install:•Carburetor
• Throttle position sensor coupler
6. Adjust: • Engine idling speedRefer to "ADJUSTING THE EN-
GINE IDLING SPEED" section in
the CHAPTER 3.
7. Insert the thin electric conductors
"2" (lead) into the throttle position
sensor coupler "1", as shown, and
connect the tester to them.
• Do not insert the electric conduc-tors more than required because
it may reduce the waterproof
function of the coupler.
• Make sure that a short-circuit
does not develop between the
terminals because it may cause
damage to electrical compo-
nents.
8. Start the engine.
9. Adjust:• Throttle position sensor output voltage
Adjustment steps:
a. Adjust the installation angle of the throttle position sensor "1" to ob-
tain the specified output voltage.
Tester (+) lead
→Blue lead "1"
Tester (-) lead →Black lead "2"
Throttle po- sition sen-
sor coil
resistance Tester se-
lector posi- tion
4–6 k Ω at
20°C (68 °F) k
Ω×1
Tester (+) lead →Yellow lead "1"
Tester (-) lead →Black lead "2"
Throttle posi-
tion sensor coil
variable resis- tance Tester
selec-
tor po- sition
Full
closed Full
opene
d
kΩ×1
Zero –3
k Ωat
20°C
(68 °F) 4–6
k Ωat
20 °C
(68 °F)
Tester (+) lead →Yellow lead "3"
Tester (-) lead →Black lead "4"

7-17
THROTTLE POSITION SENSOR SYSTEM
Measure the output voltage accurate-
ly with a digital electronic voltmeter
that gives an easy reading of a small
voltage.
10. Put the aligning marks "a" on the throttle position sensor and car-
buretor.
11. Stop the engine.
12. Remove the carburetor.
13. Tighten: • Screw (throttle position sensor) "1"
Tighten the screw (throttle position
sensor) using the T25 bit.
14. Install the carburetor.
CHECKING THE THROTTLE
POSITION SENSOR INPUT
VOLTAGE
1. Disconnect the throttle position sensor coupler.
2. Start the engine.
3. Inspect: • Throttle position sensor input volt-age
Out of specification →Replace the
CDI unit. Throttle po-
sition sen-
sor output voltage Tester se-
lector posi- tion
0.58–0.78 V DCV
Tester (+) lead →Blue lead "1"
Tester (-) lead →Black/Blue lead
"2"
Throttle po-sition sen- sor input voltage Tester se-
lector posi-
tion
4–6 V DCV-20

7-19
LIGHTING SYSTEM
CHECKING THE TAILLIGHT
(LEDs)
1. Disconnect the taillight coupler.
2. Connect two jumper leads "1" from the battery terminals to the
respective coupler terminal as
shown.
3. Check: • LED (for proper operation)Does not light →Replace the tail-
light assembly.
• A wire that is used as a jumper lead must have at least the same
capacity of the battery lead, oth-
erwise the jumper lead may burn.
• This check is likely to produce sparks, therefore, make sure no
flammable gas or fluid is in the
vicinity.
CHECKING THE AC MAGNETO
1. Inspect:• Lighting coil resistance
Out of specification →Replace.
CHECKING THE RECTIFIER/
REGULATOR
1. Connect the battery leads.
2. Start the engine.
3. Turn on the headlight and taillight by turning on the light switch. 4. Inspect:
• Out-put voltageOut of specification →Replace
rectifier/regulator.
Battery (+) terminal →Blue lead
"2"
Battery (-) terminal →Black lead
"3"
Tester (+) lead →Yellow lead "1"
Tester (-) lead →Ground "2"
Lighting
coil resis-
tance Tester se-
lector posi-
tion
0.224–0.336 Ω at 20 °C (68 °F) Ω × 1
Tester (+) lead
→Yellow lead "1"
Tester (-) lead →Black lead "2"
Out-put voltage Tester se-
lector posi- tion
12.5–13.5 V at 5,000 r/ min ACV-20