Yamaha YZF-R125 Service Manual: Starting failures

Yamaha YZF-R125 Service Manual / Troubleshooting / 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:

Checking the transmission
1. Measure: Main axle runout (with a centering device and dial gauge "1") Out of specification Replace the main axle. 2. Measure: Drive axle runout (with a centering device and dial gauge "1") Out of specification Replace the drive axle. 3. Check: Transmiss ...

Throttle position sensor
1. Check: Throttle position sensor a. Connect the digital circuit tester to the terminals of the throttle body sensor assembly coupler as shown. Positive tester probe → gray/red terminal "1" Negative tester probe → gray/black terminal "2" b. Measure the throttle pos ...

Checking the thermostat
1. Check: Thermostat Does not open at 80.5-83.5 C (176.9-182.3 F) Replace. a. Suspend the thermostat "1" in a container "2" filled with water. b. Slowly heat the water "3". c. Place a thermometer "4" in the water. d. While stirring the water, observe the thermostat and th ...