Yamaha YFM7FGPW Service Manual page 108

MEASURING THE COMPRESSION PRESSURE
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, squirt a few drops of
oil into the cylinder and measure again.
Refer to the following table.
Compression pressure
(with oil applied into the cylinder)
Reading
Higher than
without oil
Same as without
oil
L LLL L LLL L L LLL L
8. Install:
• spark plug
9. Connect:
• spark plug cap
10.Install:
• V-belt cooling duct 2
Refer to "ENGINE REMOVAL" in chapter 4.
• right side panel
Refer to "SEAT AND SIDE PANELS".
3 - 27
CHK
ADJ
Diagnosis
Piston ring(s) wear
or damage →
Repair.
Piston, valves,
cylinder head
gasket or piston
rings possibly
defective → Repair.
L LLL L L LLL L L LLL L LLL
13 Nm (1.3 m · kg, 9.4 ft · lb)