9
Testing Engine
Compression
To test engine compression, use the following procedure.
1. Remove the high tension lead(s) from the spark
plug(s).
2. Using compressed air, blow any debris from around
the spark plug(s).
3. Remove the spark plug(s); then attach the high ten-
sion lead(s) to the plug(s) and ground the plug(s) on
the cylinder head(s) well away from the spark plug
hole(s).
4. Attach the Compression Tester Kit.
NOTE: The engine should be warm (operating tem-
perature) and the battery fully charged for an accu-
rate compression test. Throttle must be in the
wide-open throttle (WOT) position. In the event the
engine cannot be run, cold values are included.
5. While holding the throttle lever in the full-open posi-
tion, crank the engine over with the electric starter
until the gauge shows a peak reading (five to 10
compression strokes).
6. If compression is abnormally low, inspect the
following items.
A. Verify starter cranks engine over at normal speed
(approximately 400 RPM).
B. Gauge functioning properly.
C. Throttle lever in the full-open position.
D. Valve/tappet clearance correct.
E. Engine warmed up.
F. Intake not restricted.
NOTE: To service valves, see Engine/Transmission -
Servicing Top-Side Components.
7. Pour 29.5 ml (1 fl oz) of oil into the spark plug hole,
reattach the gauge, and retest compression.
8. If compression is now evident, service the piston
rings (see Engine/Transmission - Servicing Top-Side
Components).
Spark Plugs
A light brown insulator indicates that a plug is correct. A
white or dark insulator indicates that the engine may need
to be serviced. To maintain a hot, strong spark, keep the
plug free of carbon.
ATV-0051
Adjust the gap to correct specification (see General Infor-
mation - General Specifications for proper type and gap).
Use a feeler gauge to check the gap.
ATV0052
When installing the spark plug, be sure to tighten it
securely. A new spark plug should be tightened 1/2 turn
once the washer contacts the cylinder head. A used spark
plug should be tightened 1/8 - 1/4 turn once the washer
contacts the cylinder head.
Muffler/Spark Arrester
At the intervals shown in the Periodic Maintenance
Chart, clean the spark arrester using the following proce-
dure.
! WARNING
Always wear safety glasses when using compressed
air.
COMPRESSION
PSI Hot (WOT)
PSI Cold (WOT)
(Front)
125-145
80-120
(Rear)
165-185
150-190
CAUTION
Before removing a spark plug, be sure to clean the area
around the spark plug. Dirt could enter engine when
removing or installing the spark plug.
! WARNING
Wait until the muffler cools to avoid burns.
