Yamaha XF50W Service Manual page 78

MEASURING THE COMPRESSION PRESSURE
•••••••••••••••••••••••
a. Set the main switch to "ON".
b. With the throttle wide open, crank the en-
gine until the reading on the compression
gauge stabilizes.
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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
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 without oil
Same as without oil
•••••••••••••••••••••••
8. Remove:
• compression gauge
9. Install:
• spark plug
X I 13Nm(1.3m
10. Connect:
• spark plug cap
11. Install:
• panel
Refer to"FOOTREST BOARD AND IN-
NER FENDER".
3-23
-» Eliminate.
Diagnosis
Piston ring(s) wear or
damage -»Repair.
Piston ring(s), valves,
cylinder head gasket or
piston possibly defec-
tive -» Repair.
* kg9.4ft* lb)