Yamaha YZF-R125 Service Manual: Starting failures
Engine
1. Cylinder and cylinder head
- Loose spark plug
- Loose cylinder head or cylinder
- Damaged cylinder head gasket
- Damaged cylinder gasket
- Worn or damaged cylinder
- Incorrect valve clearance
- Improperly sealed valve
- Incorrect valve-to-valve-seat contact
- Incorrect valve timing
- Faulty valve spring
- Seized valve
2. Piston and piston ring(s)
- Improperly installed piston ring
- Damaged, worn or fatigued piston ring
- Seized piston ring
- Seized or damaged piston
3. Air filter
- Improperly installed air filter
- Clogged air filter element
4. Crankcase and crankshaft
- Improperly assembled crankcase
- Seized crankshaft
Fuel system
1. Fuel tank
- Empty fuel tank
- Clogged fuel filter
- Deteriorated or contaminated fuel
2. Fuel pump
- Faulty fuel pump
3. Throttle body
- Deteriorated or contaminated fuel
- Sucked-in air
Electrical system
1. Battery
- Discharged battery
- Faulty battery
2. Fuse(s)
- Blown, damaged or incorrect fuse
- Improperly installed fuse
3. Spark plug
- Incorrect spark plug gap
- Incorrect spark plug heat range
- Fouled spark plug
- Worn or damaged electrode
- Worn or damaged insulator
- Faulty spark plug cap
4. Ignition coil
- Cracked or broken ignition coil body
- Broken or shorted primary or secondary coils
- Faulty spark plug lead
5. Ignition system
- Faulty ECU
- Faulty crankshaft position sensor
- Broken generator rotor woodruff key
6. Switches and wiring
- Faulty main switch
- Faulty engine stop switch
- Broken or shorted wiring
- Faulty neutral switch
- Faulty start switch
- Faulty sidestand switch
- Faulty clutch switch
- Improperly grounded circuit
- Loose connections
7. Starting system
- Faulty starter motor
- Faulty starter relay
- Faulty starting circuit cut-off relay
- Faulty starter clutch
General information
NOTE:
The following guide for troubleshooting does not
cover all the possible causes of trouble. It should
be helpful, however, as a guide to basic troubleshooting.
Refer to the relative procedu ...
Incorrect engine idling speed
Engine
1. Cylinder and cylinder head
Incorrect valve clearance
Damaged valve train components
2. Air filter
Clogged air filter element
Fuel system
1. Throttle body
Damaged or loo ...
Other materials:
Types of bulbs
The bulbs used on this vehicle are shown in the
illustration.
Bulbs "a" and "b" are used for the headlights
and usually use a bulb holder that must be detached
before removing the bulb. The majority
of these types of bulbs can be removed from
their respective socket by turning them coun ...
Installing the rear brake caliper
1. Install:
Brake caliper "1"
Copper washers
Brake hose "2"
Union bolt "3"
WARNINGProper brake hose routing is essential to
insure
safe vehicle operation. Refer to "CABLE
ROUTING" on page 2-33.
CAUTION:When installing the brake hose onto the
brake calip ...
Battery
A poorly maintained battery will corrode
and discharge quickly. The electrolyte
level, battery lead connections and
breather hose routing should be
checked before each ride and at the intervals
specified in the periodic maintenance
and lubrication chart.
WARNING
Electrolyte is pois ...