Yamaha YZF-R125 Owners Manual: Checking the spark plug

The spark plug is an important engine component, which is easy to check. Since heat and deposits will cause any spark plug to slowly erode, the spark plug should be removed and checked in accordance with the periodic maintenance and lubrication chart. In addition, the condition of the spark plug can reveal the condition of the engine.

To remove the spark plug

  1. Remove cowling A.
  2. Remove the spark plug cap.


  1. Spark plug cap

  1. 3. Remove the spark plug as shown, with the spark plug wrench included in the owner's tool kit.


  1. Spark plug wrench

To check the spark plug

  1. Check that the porcelain insulator around the center electrode of the spark plug is a medium-to-light tan (the ideal color when the vehicle is ridden normally).

TIP
If the spark plug shows a distinctly different color, the engine could be operating improperly. Do not attempt to diagnose such problems yourself. Instead, have a Yamaha dealer check the vehicle.

  1. Check the spark plug for electrode erosion and excessive carbon or other deposits, and replace it if necessary.
Specified spark plug:

NGK/CR8E

To install the spark plug

  1. Measure the spark plug gap with a wire thickness gauge and, if necessary, adjust the gap to specification.


  1. Spark plug gap

Spark plug gap:

0.7-0.8 mm (0.028-0.031 in)
  1. Clean the surface of the spark plug gasket and its mating surface, and then wipe off any grime from the spark plug threads.
  2. Install the spark plug with the spark plug wrench, and then tighten it to the specified torque.
Tightening torque:

Spark plug:

12.5 Nm (1.25 m.kgf, 9.0 ft.lbf)

TIP
If a torque wrench is not available when installing a spark plug, a good estimate of the correct torque is 1/4-1/2 turn past finger tight. However, the spark plug should be tightened to the specified torque as soon as possible.

  1. Install the spark plug cap.
  2. Install the cowling.
    Removing and installing the cowlings and panel
    Removing and installing the cowlings and panel Cowling A Cowling B Cowling C Cowling D Panel A The cowlings and panel shown need to be removed to perform some of the maintenance ...

    Engine oil and oil filter element
    The engine oil level should be checked before each ride. In addition, the oil must be changed and the oil filter element replaced at the intervals specified in the periodic maintenance and lub ...

    Other materials:

    Installing the front wheel (disc)
    1. Install: Front brake disc NOTE: Be sure to install the front brake disc with the arrow mark "a" on the disc facing out. Tighten the brake disc bolts in stages and in a crisscross pattern. 2. Check: Front brake disc Refer to "CHECKING THE FRONT BRAKE DISC" on page 4 ...

    Checking the piston pin
    1. Check: Piston pin Blue discoloration/grooves  Replace the piston pin and then check the lubrication system. 2. Measure: Piston pin outside diameter "a" Out of specification Replace the piston pin. 3. Measure: Piston pin bore diameter "b" Out of specifica ...

    Checking the speed sensor
    1. Check: Speed sensor output voltage Out of specification → Replace. a. Connect the pocket tester (DC 20 V) to the speed sensor coupler (wire harness end) as shown. Positive tester probe gray "1" Negative tester probe gray/black "2" b. Set the main switch to "ON". c. ...

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