Yamaha YZF-R125 Service Manual: 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 loose throttle body joint
- Improperly adjusted engine idling speed (idle adjusting screw)
- Improper throttle cable free play
- Flooded throttle body
- Faulty air induction system
Electrical system
1. Battery
- Discharged battery
- Faulty battery
2. 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
3. Ignition coil
- Broken or shorted primary or secondary coils
- Faulty spark plug lead
- Cracked or broken ignition coil
4. Ignition system
- Faulty ECU
- Faulty crankshaft position sensor
- Broken generator rotor woodruff key
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 c ...
Poor medium-and-high-speed performance
Refer to "STARTING FAILURES" on page 9-1.
Engine
1. Air filter
Clogged air filter element
Fuel system
1. Fuel pump
Faulty fuel pump
Faulty gear shifting
Shifting is difficult
Refer ...
Other materials:
Checking the shift shaft
1. Check:
Shift shaft
Bends/damage/wear Replace.
Shift shaft spring
Damage/wear Replace.
Checking the stopper lever
1. Check:
Stopper lever
Bends/damage Replace.
Roller turns roughly Replace
the stopper
lever.
Stopper lever spring
Damage/wear Replace.
...
Checking the cylinder and piston
1. Check:
Piston wall
Cylinder wall
Vertical scratches Replace the
cylinder,
and replace the piston and piston rings as a
set.
2. Measure:
Piston-to-cylinder clearance
a. Measure cylinder bore "C" with the cylinder
bore gauge.
NOTE:
Measure cylinder bore "C" by takin ...
Checking the stator coil
1. Disconnect:
Stator coil coupler
(from the wire harness)
2. Check:
Stator coil resistance
Out of specification → Replace the
crankshaft
position sensor/stator assembly.
a. Connect the pocket tester ( ×
1) to the stator
coil coupler as shown.
b. Measure the sta ...