sensor YAMAHA YZ250F 2008 User Guide

6-6
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 POSITION 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 speed
Refer 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.
ŒDo 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) kΩ×1
Tester (+) lead→Yellow lead "1"
Tester (-) lead
→Black lead "2"
Throttle position sensor coil vari-
able resistance Tester
selec-
tor po- sition
Full
closed Full
opened
k
Ω×1
Zero –3
kΩat
20°C
(68 °F) 4–6
kΩat
20 °C
(68 °F)
Tester (+) lead→Yellow lead "3"
Tester (-) lead
→Black lead "4"

6-7
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