Insufficient compression pressure will result in a loss of performance.
1. Measure:
- Valve clearance
Out of specification → Adjust.
Refer to "Adjusting the valve clearance".
2. Start the engine, warm it up for several minutes, and then turn it off.
3. Remove:
- Fuel tank
Refer to "Fuel tank".
- Air filter case
Refer to "Air filter case".
- Air filter case duct
Refer to "Air induction system".
4. Remove:
- Ignition coils
- Spark plugs
Notice: Before removing the spark plugs, use compressed air to blow away any dirt accumulated in the spark plug wells to prevent it from falling into the cylinders.
5. Install:
- Compression gauge "1"
Compression gauge 90890-03081.
Engine compression tester YU-33223.
6. Measure:
- Compression pressure
Out of specification → Refer to steps (c) and (d).
Standard compression pressure (at sea level) 1480 kPa/350 r/min (14.8 kgf/ cm²/350 r/min, 210.5 psi/350 r/ min). Minimum-Maximum 1290-1660 kPa/350 r/min (12.9-16.6 kgf/cm²/350 r/min, 183.5-236.1 psi/350 r/min).
a. Set the main switch to "ON".
b. With the throttle wide open, crank the engine until the reading on the compression gauge stabilizes.
Warning: The difference in compression pressure between cylinders should not exceed 100 kPa (1 kgf/cm², 14 psi).
Compression gauge 90890-03081. Engine compression tester YU-33223.
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.
| Compression pressure (with oil applied into the cylinder) | |
| Reading | Diagnosis |
| Higher than without oil | Piston ring(s) wear or damage → Replace. |
| Same as without oil | Piston, valves or cylinder head gasket possibly defective → Replace. |
7. Install:
- Spark plugs
- Ignition coils
Spark plug 13 Nm (1.3 m·kgf, 9.4 ft·lbf).
8. Install:
- All removed parts
For installation, reverse the removal procedure.