Yamaha YFM45FAR, YFM450FAR. Service Manual - part 24

9 - 37

–

+

ELEC

SIGNAL SYSTEM

4.Horn does not sound. (for Europe and

Oceania)

CORRECT

1.Horn switch

Refer to “CHECKING THE SWITCH”.

INCORRECT

Replace horn switch.

2.Voltage

●

Connect the pocket tester (DC 20 V) to the
horn connector at the horn terminal.

Tester (+) lead 

→

 Pink lead 

1

 

Tester (–) lead 

→

 Frame ground

MEETS
SPECIFICATION

HORN IS NOT
SOUNDED

●

Turn the main switch to “ON”.

●

Push the horn switch.

●

Check for voltage (12 V) on the “Pink” lead
at the horn terminal.

3.Horn

●

Disconnect the black lead at the horn
terminal.

●

Connect a jumper lead 

1

 to the horn

terminal and ground the jumper lead.

●

Turn the main switch to “ON”.

●

Push the horn switch.

Adjust or replace horn.

OUT OF SPECIFICATION

The wiring circuit from the main switch to the
bulb socket connector is faulty, repair it.

HORN IS SOUNDED

Horn is good.

9 - 38

–

+

ELEC

COOLING SYSTEM

COOLING SYSTEM

CIRCUIT DIAGRAM

W

/

B

B

B

/

R

B

/

R

B

W

/

B

C

D

OB

BO

LB

BL

YB

r

BB

B

/

Y

B

BB

(GRA

Y)

(GRA

Y)

D

WIRE HARNESS

SUB-WIRE 

HARNESS 4

Br

Sb

L

/

B

R

/

B

Br

/

B

B

/

Y

L

/

B

Sb

Br

B

/

Y

Br

/

B

R

/

B

Br

Y

L

L

/

B

GB

LY

R

/

Y

BG

L

/

B

WS

b

G

/

L

L

/

WB

/

RW

/

L

G

/

L

Sb

W

W

/

LB

/

RL

/

W

W

/

R

Sb

L

/

WG

/

W

Sb

W

/

R

G

/

WL

/

W

W

/

B

L

/

Y

Br

W

/

R

L

/

Y

W

/

B

W

/

R

Br

W

/

G

R

W

/

RW

/

G

R

W

/

G

W

/

L

W

/

R

RB

r

R

Br

/

L

Br

R

Br

/

L

R

L

/

GL

/

R

L

/

B

Sb

L

/

RL

/

G

Sb

L

/

B

R

L

/

WL

/

B

R

/

BL

/

W

OB

B

/

Y

R

W

/

RW

/

G

W

Y

/

B

B

/

RG

/

L

G

/

WW

/

B

Sb

G

/

R

(BLA

CK)

(BLA

CK)

(BLA

CK)

C

WIRE HARNESS

SUB-WIRE 

HARNESS 3

B

WIRE HARNESS

SUB-WIRE 

HARNESS 2

A

WIRE HARNESS

SUB-WIRE 

HARNESS 1

(BLA

CK)

(BLA

CK)

(BLA

CK)

(GRA

Y)

(GRA

Y)

(GRA

Y)

(GRA

Y)

(BLA

CK)

(BLA

CK)

Gy

G

/

R

Br

B

G

/

R

Gy

BB

r

(GRA

Y)

(GRA

Y)

W

WW

W

WW

OFF

ON

OFF

2WD

4WD

LOCK

W

/

G

Br

/

L

R

/

G

L

/

B

G

/

W

G

/

W

L

/

W

Br

Br

W

/

R

W

/

G

R

W

/

G

W

/

R

L

/

W

L

/

Y

R

/

B

G

/

W

Y

/

B

G

/

R

Sb

G

/

L

W

/

B

B

/

R

B

/

Y

B

/

Y

L

/

Y

R

/

G

Br

/

R

B

/

R

W

/

B

G

/

L

G

/

R

W

/

L

W

/

L

R

Br

Sb

O

C

B

O

B

W

W

B

B

B

W

B

W

W

W

W

W

W

R

R

R

R

B

WW

W

R

B

B

PUSH

_

R

R

B

B

B

B

B

B

R

R

R

D

W

/

R

W

/

R

D

L

/

W

B

/

R

B

/

R

L

/

W

D

A

Br

/

B

Br

/

B

Br

/

B

B

B

W

/

B

W

/

B

W

/

B

A

Sb

Sb

O

/

R

P

B

/

W

L

/

Y

W

B

G

/

R

R

/

G

B

G

/

RR

/

G

B

Y

G

B

YG

B

YG

B

B

/

Y

Br

/

R

Br

/

R

L

/

R

B

(BLACK)

Br

/

B

Br

/

R

Br

/

R

L

/

G

B

(BLACK)

Br

/

R

L

/

R

B

/

Y

Br

/

R

B

Br

/

R

L

/

G

Br

/

B

B

B

B

B

B

Br

Sb

L

/

B

L

/

G

Br

B

/

Y

Sb

L

/

B

B

/

Y

L

/

R

Y

/

B

Br

/

R

L

/

R

Gy

Gy

G

/

R

Br

/

B

W

/

B

B

B

/

YB

/

R

B

L

/

B

Sb

Br

B

B

B

B

A

Y

/

B

Gy

Br

/

R

L

/

R

Br

/

L

Br

/

R

Br

/

L

L

/

B

R

/

B

Br

/

L

R

/

W

R

/

W

Br

/

L

R

/

Y

Br

/

L

Br

R

/

B

R

/

B

R

/

Y

P

B

B

B

G
Y

G
Y

B

L

L

L

PUSH

_

Br

B

B

P

(BLACK)

(BLACK)

R

/

B

R

/

W

R

/

B

R

/

W

B

G
Y

B

L
Y

Y

G

B

(DARK GRAY)

(BLACK)

(BLACK)

L

R

/

B

Br

Y

YB

r

BB

(BLACK)

(BLACK)

Br

Y

Br

B

Br

B

1

2

3

4

5

6

7

8

9

0

A

B

C

D

E

F

G

HI

J

K

L

M

O

P

Q

R

ST

U

V

W

Y

\

]

b

d

e

i

g

j

k

h

b

^a

X

Z

[

c

f

N

3

Main s

witc

h

5

Battery

6

Main

 fu

se

c

Circuit

 br

eaker

 (f

an

 mo

to

r)

d

Thermo s

witch 2

e

Fan

 m

o

tor

9 - 39

–

+

ELEC

COOLING SYSTEM

TROUBLESHOOTING 

Procedure

Check:
1.Fuse (main)
2.Battery
3.Main switch
4.Fan motor
5.Circuit breaker (fan motor)

IF THE FAN MOTOR DOES NOT MOVE:

6.Thermo switch 2
7.Wiring connection

(the entire cooling system)

NOTE:

●

Remove the following part(s) before
troubleshooting.

1)Seat
2)Front carrier
3)Front fender

●

Use the following special tool(s) for
troubleshooting.

Pocket tester:

P/N. YU-03112, 90890-03112

EB802011

CONTINUITY

1.Fuse (main)

Refer to “CHECKING THE SWITCH”.

NO CONTINUITY

Replace the fuse.

EB802012

CORRECT

2.Battery

●

Check the battery condition.
Refer to “CHECKING THE BATTERY” in
CHAPTER 3.

Open-circuit voltage:

12.8 V or more at 20 °C (68 °F)

INCORRECT

●

Clean the battery terminals.

●

Recharge or replace the battery.

CORRECT

3.Main switch

Refer to “CHECKING THE SWITCH”.

*

INCORRECT 

Replace the main switch.

9 - 40

–

+

ELEC

COOLING SYSTEM

C0NTINUITY

TURNS

4.Fan motor

●

Disconnect the fan motor coupler.

●

Connect the battery (12 V) as shown.

Battery (+) lead 

→

 Blue terminal 

1

 

Battery (–) lead 

→

 Black terminal 

2

 

●

Check the operation of the fan motor.

*

DOES NOT TURN

Replace the fan motor.

MEETS
SPECIFICATION

5.Circuit breaker (fan motor)

●

Remove the circuit breaker from the wire
harness.

●

Connect the pocket tester (

Ω

 

×

 1) to the

circuit breaker.

Circuit breaker resistance:

Zero 

Ω

 at 20 °C (68 °F)

*

OUT OF SPECIFICATION

Replace the circuit breaker.

9 - 41

–

+

ELEC

COOLING SYSTEM

C0NTINUITY

GOOD
CONDITION

6.Thermo switch 2

●

Remove the thermo switch 2 from the
radiator.

●

Connect the pocket tester (

Ω

 

×

 10) to the

thermo switch 2 

1

.

●

Immerse the thermo switch 2 in coolant 

2

.

●

Check the thermo switch 2 for continuity.
While heating the coolant use a
thermometer 

3

 to record the

temperatures.

Test 
step

Coolant temperature

Continuity

Thermo switch 2

1

Less than 86 ± 3 °C

(186.8 ± 5.4 °F)

NO

2

More than 86 ± 3 °C

(186.8 ± 5.4 °F)

YES

3

More than 80 ± 3 °C

(176 ± 5.4 °F)

YES

4

Less than 80 ± 3 °C

(176 ± 5.4 °F)

NO

Test steps 1 & 2: Heating phase
Test steps 3 & 4: Cooling phase

È

The thermo switch 2 circuit is open and the
radiator fan is off.

É

The thermo switch 2 circuit is closed and the
radiator fan is on.

WARNING

Handle the thermo switch 2 with special
care.
Never subject it to a strong shock or
allow it to be dropped. Should it be
dropped, it must be replaced.

T

 

R

.

.

Thermo switch 2:

28 Nm (2.8 m • kg, 20 ft • lb)
Three bond sealock

®

 #10

*

*

É

È

80 ± 3 ˚C

(176 ± 5.4 ˚F)

86 ± 3 ˚C

(186.8 ± 5.4 ˚F)

BAD CONDITION

Replace the thermo switch 2.

9 - 42

–

+

ELEC

COOLING SYSTEM

C0NTINUITY

EB803028

CORRECT

7.Wiring connection

●

Check the connections of the entire starting
system.
Refer to “CIRCUIT DIAGRAM”.

This circuit is not faulty.

*

POOR CONNECTION

Properly connect the cooling system.

9 - 43

–

+

ELEC

2WD/4WD SELECTING SYSTEM

2WD/4WD SELECTING SYSTEM

CIRCUIT DIAGRAM

W

/

B

B

B

/

R

B

/

R

B

W

/

B

C

D

OB

BO

LB

BL

YB

r

BB

B

/

Y

B

BB

(GRA

Y)

(GRA

Y)

D

WIRE HARNESS

SUB-WIRE 

HARNESS 4

Br

Sb

L

/

B

R

/

B

Br

/

B

B

/

Y

L

/

B

Sb

Br

B

/

Y

Br

/

B

R

/

B

Br

Y

L

L

/

B

GB

LY

R

/

Y

BG

L

/

B

WS

b

G

/

L

L

/

WB

/

RW

/

L

G

/

L

Sb

W

W

/

LB

/

RL

/

W

W

/

R

Sb

L

/

WG

/

W

Sb

W

/

R

G

/

WL

/

W

W

/

B

L

/

Y

Br

W

/

R

L

/

Y

W

/

B

W

/

R

Br

W

/

G

R

W

/

RW

/

G

R

W

/

G

W

/

L

W

/

R

RB

r

R

Br

/

L

Br

R

Br

/

L

R

L

/

GL

/

R

L

/

B

Sb

L

/

RL

/

G

Sb

L

/

B

R

L

/

WL

/

B

R

/

BL

/

W

OB

B

/

Y

R

W

/

RW

/

G

W

Y

/

B

B

/

RG

/

L

G

/

WW

/

B

Sb

G

/

R

(BLA

CK)

(BLA

CK)

(BLA

CK)

C

WIRE HARNESS

SUB-WIRE 

HARNESS 3

B

WIRE HARNESS

SUB-WIRE 

HARNESS 2

A

WIRE HARNESS

SUB-WIRE 

HARNESS 1

(BLA

CK)

(BLA

CK)

(BLA

CK)

(GRA

Y)

(GRA

Y)

(GRA

Y)

(GRA

Y)

(BLA

CK)

(BLA

CK)

Gy

G

/

R

Br

B

G

/

R

Gy

BB

r

(GRA

Y)

(GRA

Y)

W

WW

W

WW

OFF

ON

OFF

2WD

4WD

LOCK

W

/

G

Br

/

L

R

/

G

L

/

B

G

/

W

G

/

W

L

/

W

Br

Br

W

/

R

W

/

G

R

W

/

G

W

/

R

L

/

W

L

/

Y

R

/

B

G

/

W

Y

/

B

G

/

R

Sb

G

/

L

W

/

B

B

/

R

B

/

Y

B

/

Y

L

/

Y

R

/

G

Br

/

R

B

/

R

W

/

B

G

/

L

G

/

R

W

/

L

W

/

L

R

Br

Sb

O

C

B

O

B

W

W

B

B

B

W

B

W

W

W

W

W

W

R

R

R

R

B

WW

W

R

B

B

PUSH

_

R

R

B

B

B

B

B

B

R

R

R

D

W

/

R

W

/

R

D

L

/

W

B

/

R

B

/

R

L

/

W

D

A

Br

/

B

Br

/

B

Br

/

B

B

B

W

/

B

W

/

B

W

/

B

A

Sb

Sb

O

/

R

P

B

/

W

L

/

Y

W

B

G

/

R

R

/

G

B

G

/

RR

/

G

B

Y

G

B

YG

B

YG

B

B

/

Y

Br

/

R

Br

/

R

L

/

R

B

(BLACK)

Br

/

B

Br

/

R

Br

/

R

L

/

G

B

(BLACK)

Br

/

R

L

/

R

B

/

Y

Br

/

R

B

Br

/

R

L

/

G

Br

/

B

B

B

B

B

B

Br

Sb

L

/

B

L

/

G

Br

B

/

Y

Sb

L

/

B

B

/

Y

L

/

R

Y

/

B

Br

/

R

L

/

R

Gy

Gy

G

/

R

Br

/

B

W

/

B

B

B

/

YB

/

R

B

L

/

B

Sb

Br

B

B

B

B

A

Y

/

B

Gy

Br

/

R

L

/

R

Br

/

L

Br

/

R

Br

/

L

L

/

B

R

/

B

Br

/

L

R

/

W

R

/

W

Br

/

L

R

/

Y

Br

/

L

Br

R

/

B

R

/

B

R

/

Y

P

B

B

B

G
Y

G
Y

B

L

L

L

PUSH

_

Br

B

B

P

(BLACK)

(BLACK)

R

/

B

R

/

W

R

/

B

R

/

W

B

G
Y

B

L
Y

Y

G

B

(DARK GRAY)

(BLACK)

(BLACK)

L

R

/

B

Br

Y

YB

r

BB

(BLACK)

(BLACK)

Br

Y

Br

B

Br

B

1

2

3

4

5

6

7

8

9

0

A

B

C

D

E

F

G

HI

J

K

L

M

O

P

Q

R

ST

U

V

W

Y

\

]

b

d

e

i

g

j

k

h

b

^a

X

Z

[

c

f

N

3

Main switch

5

Battery

6

Main fuse

0

CDI unit

R

Four-wheel drive fuse

S

Four-wheel drive relay 1

T

Four-wheel drive relay 2

U

Four-wheel drive relay 3

V

On-command four-wheel drive switch and 
differential gear lock switch

W

Gear motor

9 - 44

–

+

ELEC

2WD/4WD SELECTING SYSTEM

EB803020

TROUBLESHOOTING

Procedure

Check:
1.Fuse (main, four-wheel drive)
2.Battery
3.Main switch
4.Four-wheel drive relay 1
5.Four-wheel drive relay 2
6.Four-wheel drive relay 3

IF THE GEAR MOTOR FAILS TO OPERATE:

7.On-command four-wheel drive switch and 

differential gear lock switch

8.Gear motor
9.Wiring connections 

(the entire 2WD/4WD selecting system)

NOTE:

●

Remove the following part(s) before
troubleshooting:

1)Seat
2)Front carrier
3)Front fender

●

Use the following special tool(s) for
troubleshooting.

Pocket tester:

P/N. YU-03112, 90890-03112

EB802011

CONTINUITY

1.Fuse (main, four-wheel drive)

Refer to “CHECKING THE SWITCH”.

NO CONTINUITY

Replace the fuse.

EB802012

CORRECT

2.Battery

●

Check the battery condition.
Refer to “CHECKING THE BATTERY” in
CHAPTER 3.

Open-circuit voltage:

12.8 V or more at 20 °C (68 °F)

INCORRECT

●

Clean the battery terminals.

●

Recharge or replace the battery.

CORRECT

3.Main switch

Refer to “CHECKING THE SWITCH”.

*

INCORRECT

Replace the main switch.

9 - 45

–

+

ELEC

2WD/4WD SELECTING SYSTEM

C0NTINUITY

CONTINUITY

4.Four-wheel drive relay 1

●

Remove the four-wheel drive relay 1 from
the wire harness.

●

Connect the pocket tester (

Ω

 

×

 1) and the

battery (12 V) to the four-wheel drive relay
1 terminals.

Tester (+) lead 

→

 

Brown/Black terminal 

1

Tester (–) lead 

→

 Black terminal 

2

 

Battery (+) terminal 

→

 

Brown/Red terminal 

3

Battery (–) terminal 

→

 

Blue/Green terminal 

4

Tester (+) lead 

→

 

Brown/Black terminal 

1

Tester (–) lead 

→

 Brown/Red terminal 

5

 

●

Check the four-wheel drive relay 1 for
continuity.

*

NO CONTINUITY

Replace the four-wheel drive relay 1.

CONTINUITY

5.Four-wheel drive relay 2

●

Remove the four-wheel drive relay 2 from
the wire harness.

●

Connect the pocket tester (

Ω

 

×

 1) and the

battery (12 V) to the four-wheel drive relay
2 terminals.

Tester (+) lead 

→

 

Black/Yellow terminal 

1

Tester (–) lead 

→

 Black terminal 

2

 

Battery (+) terminal 

→

 

Brown/Red terminal 

3

Battery (–) terminal 

→

 

Blue/Red terminal 

4

Tester (+) lead 

→

 

Black/Yellow terminal 

1

Tester (–) lead 

→

 Brown/Red terminal 

5

 

●

Check the four-wheel drive relay 2 for
continuity.

*

NO CONTINUITY

Replace the four-wheel drive relay 2.

9 - 46

–

+

ELEC

2WD/4WD SELECTING SYSTEM

C0NTINUITY

CONTINUITY

6.Four-wheel drive relay 3

●

Remove the four-wheel drive relay 3 from
the wire harness.

●

Connect the pocket tester (

Ω

 

×

 1) and the

battery (12 V) to the four-wheel drive relay
3 terminals.

Tester (+) lead 

→

 

Brown/Red terminal 

1

Tester (–) lead 

→

 

Yellow/Black terminal 

2

Battery (+) terminal 

→

 

Brown/Red terminal 

1

Battery (–) terminal 

→

 

Yellow/Black terminal 

2

Tester (+) lead 

→

 Blue/Red terminal 

3

 

Tester (–) lead 

→

 Gray terminal 

4

 

●

Check the four-wheel drive relay 3 for
continuity.

*

NO CONTINUITY

Replace the four-wheel drive relay 3.

CORRECT

7.On-command four-wheel drive switch and

differential gear lock switch

Refer to “CHECKING THE SWITCH”.

*

INCORRECT 

Replace the on-command four-wheel drive
switch and differential gear lock switch.

9 - 47

–

+

ELEC

2WD/4WD SELECTING SYSTEM

C0NTINUITY

CORRECT

8.Gear motor

●

Disconnect the gear motor coupler.

●

Remove the gear motor from the
differential gear case.
Refer to “FRONT CONSTANT VELOCITY
JOINTS AND DIFFERENTIAL GEAR” in
CHAPTER 7.

●

Connect two C size batteries to the gear
motor terminals 

1

 (as shown illustrations).

È

Check that the pinion gear 

2

 turns

counterclockwise.

É

Check that the pinion gear 

2

 turns clockwise.

●

Make sure that the drive gear (shift fork
sliding gear) operates correctly.

NOTE:

When installing the differential gear case in
the gear motor, refer to “FRONT CONSTANT
VELOCITY JOINTS AND DIFFERENTIAL
GEAR” in CHAPTER 7.

*

INCORRECT

Replace the gear motor.

EB803028

CORRECT

9.Wiring connection

●

Check the connections of the entire 2WD/
4WD selecting system.
Refer to “CIRCUIT DIAGRAM”.

Replace the CDI unit.

POOR CONNECTION

Properly connect the 2WD/4WD selecting
system.

È

É

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10

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CHAPTER 10.

TROUBLESHOOTING

STARTING FAILURE/HARD STARTING 

.................................................. 10-1

FUEL SYSTEM  ................................................................................... 10-1
ELECTRICAL SYSTEM  ...................................................................... 10-1
COMPRESSION SYSTEM .................................................................. 10-2

POOR IDLE SPEED PERFORMANCE 

...................................................... 10-2

POOR IDLE SPEED PERFORMANCE ............................................... 10-2

POOR MEDIUM AND HIGH-SPEED PERFORMANCE 

............................. 10-2

POOR MEDIUM AND HIGH-SPEED PERFORMANCE  ..................... 10-2

FAULTY DRIVE TRAIN 

.............................................................................. 10-3

FAULTY GEAR SHIFTING 

......................................................................... 10-4

HARD SHIFTING  ................................................................................ 10-4
SHIFT LEVER DOES NOT MOVE ...................................................... 10-4
JUMPS OUT OF GEAR  ...................................................................... 10-4

FAULTY CLUTCH PERFORMANCE 

......................................................... 10-4

ENGINE OPERATES BUT MACHINE WILL NOT MOVE ................... 10-4
CLUTCH SLIPPING  ............................................................................ 10-4
POOR STARTING PERFORMANCE .................................................. 10-4
POOR SPEED PERFORMANCE ........................................................ 10-5

OVERHEATING 

.......................................................................................... 10-5

OVERHEATING .................................................................................. 10-5

FAULTY BRAKE 

........................................................................................ 10-5

POOR BRAKING EFFECT .................................................................. 10-5

SHOCK ABSORBER MALFUNCTION 

...................................................... 10-6

MALFUNCTION .................................................................................. 10-6

UNSTABLE HANDLING 

............................................................................. 10-6

UNSTABLE HANDLING ...................................................................... 10-6

LIGHTING SYSTEM 

................................................................................... 10-6

HEADLIGHT DARK ............................................................................. 10-6
BULB BURNT OUT  ............................................................................. 10-6

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10 - 1

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STARTING FAILURE/HARD STARTING

TROUBLESHOOTING

NOTE:

The following troubleshooting does not cover all the possible causes of trouble. It should be helpful,
however, as a guide to troubleshooting. Refer to the relative procedure in this manual for checking,
adjusting and replacing of parts.

STARTING FAILURE/HARD STARTING

FUEL SYSTEM 
Fuel tank

●

Empty

●

Clogged fuel filter

●

Clogged fuel strainer

●

Clogged fuel breather hose

●

Deteriorated or contaminated fuel

Fuel cock

●

Clogged fuel hose

ELECTRICAL SYSTEM 
Spark plug

●

Improper plug gap

●

Worn electrodes

●

Wire between terminals broken

●

Improper heat range

●

Faulty spark plug cap

Ignition coil

●

Broken or shorted primary/secondary

●

Faulty spark plug lead

●

Broken body

CDI system

●

Faulty CDI unit

●

Faulty pickup coil

●

Faulty charging/rotor rotation direction coil

●

Broken woodruff key

Carburetor

●

Deteriorated or contaminated fuel

●

Clogged pilot jet

●

Clogged pilot air passage

●

Sucked-in air

●

Deformed float

●

Worn needle valve

●

Improperly sealed valve seat

●

Improperly adjusted fuel level

●

Improperly set pilot jet

●

Clogged starter jet

●

Starter plunger malfunction

Air filter

●

Clogged air filter element

Switches and wiring

●

Faulty main switch

●

Faulty engine stop switch

●

Broken or shorted wiring

●

Faulty neutral switch

●

Faulty reverse switch

●

Faulty low-range switch

●

Faulty high-range switch

●

Faulty start switch

●

Faulty rear brake switch

Starter motor

●

Faulty starter motor

●

Faulty starter relay

●

Faulty starter clutch

10 - 2

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SHTG

STARTING FAILURE/HARD STARTING/POOR IDLE SPEED

PERFORMANCE/POOR MEDIUM AND HIGH-SPEED PERFORMANCE

COMPRESSION SYSTEM 
Cylinder and cylinder head

●

Loose spark plug

●

Loose cylinder head or cylinder

●

Broken cylinder head gasket

●

Broken cylinder gasket

●

Worn, damaged or seized cylinder

Piston and piston rings

●

Improperly installed piston ring

●

Worn, fatigued or broken piston ring

●

Seized piston ring

●

Seized or damaged piston

Valve, camshaft and crankshaft

●

Improperly sealed valve

●

Improperly contacted valve and valve seat

●

Improper valve timing

●

Broken valve spring

●

Seized camshaft

●

Seized crankshaft

POOR IDLE SPEED PERFORMANCE

POOR IDLE SPEED PERFORMANCE
Carburetor

●

Improperly returned starter plunger

●

Loose pilot jet

●

Clogged pilot jet

●

Clogged pilot air jet

●

Improperly adjusted idle speed 
(Throttle stop screw)

●

Improper throttle cable play

●

Flooded carburetor

Electrical system

●

Faulty spark plug

●

Faulty CDI unit

●

Faulty pickup coil

●

Faulty charging/rotor rotation direction coil

●

Faulty ignition coil

Valve train

●

Improperly adjusted valve clearance

Air filter

●

Clogged air filter element

POOR MEDIUM AND HIGH-SPEED PERFORMANCE

POOR MEDIUM AND HIGH-SPEED PERFORMANCE

Refer to “STARTING FAILURE/HARD STARTING” and “POOR IDLE SPEED PERFORMANCE-
VALVE TRAIN”.

Carburetor

●

Improper jet needle clip position

●

Improperly adjusted fuel level

●

Clogged or loose main jet

●

Deteriorated or contaminated fuel

Air filter

●

Clogged air filter element