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 clutch plates
    The following procedure applies to all of the clutch plates. 1. Check: Clutch plate Damage Replace the clutch plates as a set. 2. Measure: Clutch plate warpage (with a surface plate and thickness gauge "1") Out of specification Replace the clutch plates as a set. ...

    Removing the fuel tank
    1. Extract the fuel in the fuel tank through the fuel tank filler hole with a pump. 2. Remove: Fuel hose connector cover "1" 3. Disconnect: Fuel hose "2" CAUTION: Be sure to disconnect the fuel hose by hand. Do not forcefully disconnect the hose with tools. A ...

    Checking the coolant temperature sensor
    1. Remove: Coolant temperature sensor WARNING Handle the coolant temperature sensor with special care. Never subject the coolant temperature sensor to strong shocks. If the coolant temperature sensor is dropped, replace it. 2. Check: Coolant temper ...

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