Yamaha YZF-R125 Service Manual: Measuring the compression pressure

NOTE:

Insufficient compression pressure will result in a loss of performance.

1. Measure:

Valve clearance Out of specification →Adjust.

Refer to "ADJUSTING THE VALVE CLEARANCE" on page 3-3.

2. Start the engine, warm it up for several minutes, and then turn it off.

3. Remove:

  • Rider seat
  • Right upper side cowling Refer to "GENERAL CHASSIS" on page 4-1.

4. Remove:

  • Fuel tank Refer to "FUEL TANK" on page 7-1.

5. Disconnect:

  • Coolant temperature sensor coupler "1"
  • Spark plug cap "2"

Measuring the compression pressure


6. Remove:

  • Spark plug
CAUTION:

Before removing the spark plug, use compressed air to blow away any dirt accumulated in the spark plug well to prevent it from falling into the cylinder.

7. Install:

  • Extension "1"
  • Compression gauge "2"

Measuring the compression pressure


8. Measure:

  • Compression pressure Out of specification Refer to steps (c) and (d).

a. Set the main switch to "ON".

b. With the throttle wide open, crank the engine until the reading on the compression gauge stabilizes.

c. If the compression pressure is above the maximum specification, check the cylinder head, valve surfaces and piston crown for carbon deposits.

Carbon deposits Eliminate.

d. If the compression pressure is below the minimum specification, pour a teaspoonful of engine oil into the spark plug bore and measure again.

Refer to the following table.


9. Remove:

  • Extension
  • Compression gauge

10.Install:

  • Spark plug

11.Connect:

  • Spark plug cap
  • Coolant temperature sensor coupler

12.Install:

  • Fuel tank Refer to "FUEL TANK" on page 7-1.

13.Install:

  • Right upper side cowling
  • Rider seat Refer to "GENERAL CHASSIS" on page 4-1.
    Checking the ignition timing
    NOTE: Prior to checking the ignition timing, check the wiring connections of the entire ignition system. Make sure all connections are tight and free of corrosion. 1. Remove: Rider seat L ...

    Checking the engine oil level
    1. Stand the vehicle on a level surface. NOTE: Place the vehicle on a suitable stand. Make sure the vehicle is upright. 2. Start the engine, warm it up for several minutes, and then turn it ...

    Other materials:

    Checking the fuel sender
    1. Drain the fuel from the fuel tank. 2. Check: Fuel sender resistance Out of specification → Replace the fuel sender. a. Connect the pocket tester ( × 10) to the fuel sender coupler as shown. Positive tester probe sky blue "1" Negative tester probe orange/white " ...

    Disassembling the front fork legs
    The following procedure applies to both of the front fork legs. 1. Remove: Rubber cap Clip "1" Front fork cap "2" (with O-ring) Fork spring NOTE: Push the front fork cap in the direction of the arrow shown in the illustration to remove the clip. 2. Drain: Fork oil NOTE ...

    Installing the radiator
    1. Fill: Cooling system (with the specified amount of the recommended coolant) Refer to "CHANGING THE COOLANT" on page 3-15. 2. Check: Cooling system Leaks Repair or replace any faulty part. 3. Measure: Radiator cap opening pressure Below the specified pressure Repla ...

    2026 Copyright www.yam-r125.net |