ignition YAMAHA YZ250F 2008 User Guide

3-23
ELECTRICAL
ELECTRICAL
CHECKING THE SPARK PLUG
1. Remove:• Spark plug
2. Inspect:
• Electrode "1"Wear/damage
→Replace.
• Insulator color "2"
Normal condition is a medium to
light tan color.
Distinctly different color
→Check
the engine condition.
When the engine runs for many hours
at low speeds, the spark plug insula-
tor will become sooty, even if the en-
gine and carburetor are in good
operating condition.
3. Measure: • Plug gap "a"Use a wire gauge or thickness
gauge.
Out of specification
→Regap.
4. Clean the plug with a spark plug cleaner if necessary.
5. Tighten: • Spark plug
• Before installing a spark plug, clean the gasket surface and plug sur-
face.
• Finger-tighten "a" the spark plug before torquing to specification "b".
CHECKING THE IGNITION TIMING
1. Remove:• Timing mark accessing screw "1" 2. Attach:
• Timing light
• Inductive tachometerTo the ignition coil lead (orange
lead"1").
3. Adjust: • Engine idling speedRefer to "ADJUSTING THE EN-
GINE IDLING SPEED" section.
4. Check: • Ignition timing
Visually check the stationary
pointer "a" is within the firing
range "b" on the rotor.
Incorrect firing range
→Check ro-
tor and pickup assembly.
5. Install: • Timing mark accessing screw
Spark plug gap:
0.7–0.8 mm (0.028–
0.031 in)
Spark plug: 13 Nm (1.3 m•kg, 9.4
ft•lb)
Timing light:YM-33277-A/90890-
03141

4-51
ENGINE REMOVAL
ENGINE REMOVAL
REMOVING THE ENGINEOrder Part name Q'ty Remarks Hold the machine by placing the suitable stand
under the frame. Refer to "HANDLING NOTE".
Seat and fuel tank Refer to "SEAT, FUEL TANK AND SIDE
COVERS" section.
Carburetor Refer to "CARBURETOR" section.
Exhaust pipe and silencer Refer to "EXHAUST PIPE AND SILENCER"
section.
Clutch cable Disconnect at the engine side.
Radiator Refer to "RADIATOR" section.
Shift pedal Refer to "KICK SHAFT AND SHIFT SHAFT"
section.
Cylinder head breather hose Refer to "CAMSHAFTS" section.
Drain the engine oil. Refer to "CHANGING THE ENGINE OIL"
section in the CHAPTER 3.
Oil hose and oil tank breather hose Refer to "OIL PUMP" section.
Ignition coil
Disconnect the CDI magneto lead.
Right engine guard

6-1
ELECTRICAL COMPONENTS AND WIRING DIAGRAM
ELECTRICAL
ELECTRICAL
COMPONENTS AND
WIRING DIAGRAM
ELECTRICAL COMPONENTS
1. Engine stop switch
2. Throttle position sensor
3. Neutral switch4. CDI magneto
5. Ignition coil
6. Spark plug7. CDI unit
WIRING DIAGRAM
1. Engine stop switch
2. Throttle position sensor
3. Neutral switch
4. CDI magneto
5. Ignition coil
6. Spark plug
7. CDI unit COLOR CODE
BBlack
Br Brown
GGreen
LBlue
OOrange
PPink
RRed
Sb Sky blue
WWhiteYYellow
B/L Black/Blue
B/W Black/White
B/Y Black/Yellow
G/B Green/Black
L/W Blue/White
R/W Red/White
B/WB/W
B/L
B/Y
SbSb
G/B
LYLY
P
B
B
B
B
G
O
WR
P
GW
R
P
B
Br W
W
B/Y G Br
G
RR
OB
Sb Sb
Y
Y
W Y
W
GG B
P P
Br BrRR
O L
B
Sb Y
LL
B/L
B/W
B/W
G/B
B
B
B/L
L
Sb
B/L
G/B
G/B B/Y
B/Y
B/W O
B/W
BrBrP

6-2
IGNITION SYSTEM
IGNITION SYSTEM
INSPECTION STEPS
Use the following steps for checking the possibility of the malfunctioning engine being attributable to ignition system failure
and for checking the spark plug which will not spark.
*marked: Only when the ignition checker is used.
• Remove the following parts before inspection.
1. Seat
2. Fuel tank
• Use the following special tools in this inspection.
Spark gap test Spark→*Clean or replace spark plug.
No spark
↓
Check entire ignition system for connection.
(couplers, leads and ignition coil) No good→Repair or replace.
OK
↓
Check engine stop switch. No good→Replace.
OK
↓
Check ignition coil. (primary coil and secondary
coil) No good→Replace.
OK
↓
Check CDI magneto. (pickup coil and charging
coil) No good→Replace.
OK
↓
Check neutral switch. No good→Repair or replace.
OK
↓
Replace CDI unit.
Dynamic spark tester: YM-34487
Ignition checker: 90890-06754
Pocket tester:
YU-3112-C/90890-03112
6

6-3
IGNITION SYSTEM
SPARK GAP TEST
1. Disconnect the ignition coil from spark plug.
2. Remove the ignition coil cap.
3. Connect the dynamic spark tester
"1" (ignition checker "2") as
shown.
• Ignition coil "3"
• Spark plug "4"
A. For USA and CDN
B. Except for USA and CDN
4. Kick the kickstarter crank.
5. Check the ignition spark gap.
6. Start engine, and increase spark gap until misfire occurs. (for USA
and CDN only)
CHECKING THE COUPLERS,
LEADS AND IGNITION COIL
CONNECTION
1. Check: • Couplers and leads connection
Rust/dust/looseness/short-circuit
→Repair or replace.
• Ignition coil and spark plug as
they are fitted
Push in the ignition coil until it
closely contacts the spark plug
hole in the cylinder head cover.
CHECKING THE ENGINE STOP
SWITCH
1. Inspect: • Engine stop switch conduction Not conductive while it is pushed
→
Replace.
Conductive while it is freed
→Re-
place.
Set the tester selection position to
"
Ω × 1".
CHECKING THE IGNITION COIL
1. Remove the ignition coil cap.
2. Inspect:
• Primary coil resistanceOut of specification
→Replace.
3. Inspect: • Secondary coil resistanceOut of specification
→Replace. 4. Inspect:
• Sealed portion of ignition coil "a"
• Spark plug terminal pin "b"
• Threaded portion of spark plug "c"Wear
→Replace.
CHECKING THE CDI MAGNETO
1. Inspect: • Pickup coil resistanceOut of specification
→Replace.
2. Inspect: • Charging coil 1 resistanceOut of specification
→Replace.
Minimum spark gap:
6.0 mm (0.24 in)
Tester (+) lead
→Black/White
lead "1"
Tester (-) lead
→Black lead "2"
Result
Conductive (while the
engine stop switch is
pushed)
Tester (+) lead
→Orange lead "1"
Tester (-) lead
→Black lead "2"
Primary
coil resis- tance Tester se-
lector posi- tion
0.08–0.10
Ω at 20 °C
(68 °F) Ω × 1
Tester (+) lead
→Orange lead "1"
Tester (-) lead
→Spark plug termi-
nal "2"
Secondary coil resis- tance Tester se-
lector posi- tion
4.6–6.8
k
Ωat 20 °C
(68 °F) kΩ × 1
Tester (+) lead→Red lead "1"
Tester (-) lead
→White lead "2"
Pickup coil resistance Tester se-
lector posi- tion
248-372
Ω
at 20 °C (68 °F)Ω ×100
Tester (+) lead
→Brown lead "1"
Tester (-) lead
→Green lead "2"
Charging
coil 1 resis- tance Tester se-
lector posi- tion
720-1,080
Ω at 20 °C
(68 °F)Ω ×100

6-4
IGNITION SYSTEM
3. Inspect:• Charging coil 2 resistanceOut of specification
→Replace.
CHECKING THE NEUTRAL
SWITCH
1. Inspect: • Neutral switch conduction
Not conductive while it is in neutral
→
Replace.
Conductive while it is engaged
→Re-
place.
Set the tester selection position to
"
Ω × 1".
CHECKING THE CDI UNIT
Check all electrical components. If no
fault is found, replace the CDI unit.
Then check the electrical compo-
nents again. Tester (+) lead
→Pink lead "1"
Tester (-) lead
→Black lead "2"
Charging
coil 2 resis- tance Tester se-
lector posi- tion
44-66
Ω at
20 °C (68
°F)
Ω ×10
Tester (+) lead
→Sky blue lead
"1"
Tester (-) lead
→Ground "2"
Result Conductive (while gear
is in neutral)

6-5
THROTTLE POSITION SENSOR SYSTEM
THROTTLE POSITION SENSOR SYSTEM
INSPECTION STEPS
If the throttle position sensor will not operate, use the following inspection steps.
*marked: Refer to "IGNITION SYSTEM" section.
Use the following special tools in this inspection.
Check entire ignition system for connection. No good→Repair or replace.
OK
↓
Check throttle position sensor. (Throttle position
sensor coil) No good→Replace.
OK
↓
*Check CDI magneto. (Charging coil) No good→Replace.
OK
↓
Check CDI unit. (Throttle position sensor input
voltage) No good→Replace.
Pocket tester:
YU-3112-C/90890-03112