BASIC TROUBLESHOOTING
17
3. Connect tester to compressed air.
4. Adjust the regulator knob until the needle on the
gauge is in the yellow or set area of the gauge.
5. Connect the tester to the adapter.
NOTE: If the engine rotates it was not at top
dead center.
6. Check the reading on the gauge.
7. Compare the results to the following chart. See
Table 1.
Table 1:
Symptom Possible cause
Air escaping from
the breather
Worn cylinder or pis-
ton rings. Possible
blown head gasket
Air escaping from
the exhaust
Leaking exhaust valve
Air escaping from
the carburetor
Leaking intake valve
Gauge reading
low
Cylinder and piston
rings are in good con-
dition
Gauge reading
moderate
There is some wear in
the engine, but it is still
usable
Gauge reading
high
excessive wear of cyl-
inder and/or piston
rings. Engine should
be short blocked or it
could be a blown head
gasket.
Compression test
To perform a compression test:
NOTE: Compression should be in the range of
40-75 PSI (2.8-5.2 Bar).
• Disconnect the high-tension lead from the spark
plug and ground it well away from the spark plug
hole.
• Remove the spark plug using a 13/16” or 21mm
wrench. A flexible coupling or “wobbly” exten-
sion may help.
• Pull the starter rope several times to purge any
fuel or oil from the combustion chamber.
NOTE: Air compresses readily, liquid does not.
Liquid in the combustion chamber will result in
an artificially high compression reading.
1. Install a compression gauge in the spark plug
hole.
2. Confirm that the gauge is “zeroed”, then pull the
starter rope repeatedly, until the needle on the
gauge stops rising.
See Figure 2.2.
Figure 2.2
Compression gauge
Reading ~
40 PSI
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