Yamaha MIO Service Manual page 69

MEASURING THE COMPRESSION PRESSURE
6. Measure:
• compression pressure
Out of specification → Refer to steps (c)
and (d).
Compression pressure (at sea
level)
Minimum
960 kPa (9.6 kg/cm
Standard
1,100 kPa
(11 kg/cm
Maximum
1,230 kPa
(12.3 kg/cm
M MMM M MMM M M MMM
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
_
To prevent sparking, ground the spark plug
lead before cranking the engine.
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
engine of oil into the spark plug bore and
measure again.
Refer to the following table.
Compression pressure
(with oil applied into the cylinder)
Reading
Higher than with-
out oil
Same as without
oil
L LLL L LLL L L LLL
7. Install:
• spark plug
3 - 15
CHK
ADJ
2
, 136.5 psi)
2
, 156.5 psi)
2
, 174.9 psi)
M M MMM M M MMM M
Diagnosis
Piston ring(s) wear
or damage →
Repair.
Piston, valves, cyl-
inder head gasket
or piston possibly
defective → Repair.
L L LLL L L LLL L
15 Nm (1.5 m · kg, 11 ft · lb)
M MMM M MMM
L LLL L LLL