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"
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"
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:
Troubleshooting
Any of the following fail to light: headlight, high beam indicator light,
taillight, license plate light, auxiliary
light or meter light.
NOTE:
Before troubleshooting, remove the following part(s):
1. Seats
2. Fuel tank
...
Cleaning and lubricating the drive chain
The drive chain must be cleaned and
lubricated at the intervals specified in
the periodic maintenance and lubrication
chart, otherwise it will quickly wear
out, especially when riding in dusty or
wet areas. Service the drive chain as
follows.
NOTICE
The drive chain must be lubricated
...
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.
...