Yamaha YZF-R125 Service Manual: Overheating

Engine

1. Clogged coolant passages

  • Cylinder head and piston
  • Heavy carbon buildup

2. Engine oil

  • Incorrect oil level
  • Incorrect oil viscosity
  • Inferior oil quality

Cooling system

1. Coolant

  • Low coolant level

2. Radiator

  • Damaged or leaking radiator
  • Faulty radiator cap
  • Bent or damaged radiator fin

3. Water pump

  • Damaged or faulty water pump
  • Thermostat
  • Thermostat stays closed
  • Hose(s) and pipe(s)
  • Damaged hose
  • Improperly connected hose
  • Damaged pipe
  • Improperly connected pipe

Fuel system

1. Throttle body

  • Damaged or loose throttle body joint

2. Air filter

  • Clogged air filter element

Chassis

1. Brake(s)

  • Dragging brake

Electrical system

1. Spark plug

  • Incorrect spark plug gap
  • Incorrect spark plug heat range

2. Ignition system

  • Faulty ECU

Overcooling

Cooling system

1. Thermostat

  • Thermostat stays open
    Faulty clutch
    Clutch slips 1. Clutch Improperly assembled clutch Improperly adjusted clutch cable Loose or fatigued clutch spring Worn friction plate Worn clutch plate 2. Engine oil Incorrect oi ...

    Poor braking performance
    - Worn brake pad - Worn brake disc - Air in hydraulic brake system - Leaking brake fluid - Faulty brake caliper kit - Faulty brake caliper seal - Loose union bolt - Damaged brake hose - Oil or ...

    Other materials:

    Checking the cylinder head breather hose
    1. Remove: Left side panel Refer to "GENERAL CHASSIS" on page 4-1. 2. Check: Cylinder head breather hose "1" Cracks/damage → Replace. Loose connection → Connect properly. CAUTION:Make sure the cylinder head breather hose is routed correctly. ...

    Circuit diagram
    4. Main fuse 5. Main switch 9. Battery 14.Neutral switch 25.ECU (engine control unit) 31.Fuel sender 34.Rear brake light switch 35.Front brake light switch 37.Tail/brake light 38.Rear right turn signal light 39.Rear left turn signal light 40.Front right turn signal light 41.Front lef ...

    Checking the starter motor
    1. Check: Commutator Dirt Clean with 600 grit sandpaper. 2. Measure: Commutator diameter "a" Out of specification Replace the starter motor. 3. Measure: Mica undercut "a" Out of specification Scrape the mica to the proper measurement with a hacksaw blade ...

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