ignition YAMAHA YZ450F 2008 User Guide

4-49
ENGINE REMOVAL
ENGINE REMOVAL
REMOVING THE ENGINE
Order 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.
Rear shock absorber Refer to "REAR SHOCK ABSORBER" sec-
tion in the CHAPTER 5.
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 pedalRefer 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.
Ignition coil
Disconnect the CDI magneto lead.

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 unitCOLOR CODE
BBlack
Br Brown
GGreen
LBlue
O Orange
PPink
RRed
Sb Sky blue
WWhiteY Yellow
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 GBr
G RR
OB Sb Sb Y
Y
WY
W
GG
B
PP
Br BrR R
OL
B SbY LL
B/L B/W B/WG/B
B B
B/L L Sb
B/L
G/B
G/BB/Y
B/Y
B/W
O B/W
BrBrP
6

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

6-3
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 conductionNot 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 resistance
Out of specification
→Replace.
3. Inspect:
• Secondary coil resistance
Out 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 resistance
Out of specification
→Replace.
2. Inspect:
• Charging coil 1 resistance
Out 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-
tanceTester 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-
tanceTester 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
resistanceTester 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-
tanceTester se-
lector posi-
tion
720-1,080
Ω at 20 °C
(68 °F)Ω ×100

6-4
IGNITION SYSTEM
3. Inspect:
• Charging coil 2 resistance
Out 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-
tanceTester 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