20
125
-
160 cc
C
WORKSHOP MANUAL
CYLINDER HEAD, VALVES, CYLINDER, PISTON
Cylinder compression pressure
NOTE Take measurement with warm engine
Remove spark plug cap (A) and spark plug.
Fit pressure gauge in spark plug bore to measure compression.
Turn over engine with starter motor and throttle body fully open.
NOTE The pressure gauge and its components must be assembled
in such a way as to avoid pressure losses.
Prolonged use of the starter motor will drain the battery: do
not run starter motor for more than 5 seconds at a time.
Compression pressure
: 700 kPa (7 bar) @ 260 RPM
If compression is too high, check for carbon deposits on the piston crown
or in the combustion chamber.
If pressure is too low, pour a little engine oil into cylinder through spark
plug bore and check measurement again.
Compare the two pressure readings; if pressure increased after adding
oil, measure cylinder, piston and piston rings. If pressure is unchanged,
check cylinder head and valves.
The problem could be:
• Pressure escaping from valves (blow-by)
• Incorrect valves clearance
A
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A