Service
This portion of the manual is still under development. If you have questions
please call the Cobra technical support line at 517 437 9100.
Engine Service
One method for determining whether the top end of your engine needs rebuilt is
to perform a WOT (Wide Open Throttle) kicking compression test. Before
performing the procedure please read the caution notes below.
CAUTION:
There appears to be a wide range of variability in reading compression
gauges across the country.
The head volume of this Cobra Motorcycle is very small and so requires many
kicks ~20 before you establish the most accurate reading possible.
Because of the geometry of the spark plug used in this Cobra Motorcycle, the
adapter used with your compression tester must have a similar volume
protruding into the combustion chamber to establish an accurate value.
Length of hose on the compression tester will affect the reading. The shorter
the hose length the more accurate your reading will be.
Because of these difficulties in measuring an absolute compression value, a
useful relative value can be achieved by testing your bike’s compression with
your own particular gauge after a new top end or when the bike is new so that
you know what your particular gauge reads on a ‘fresh’ engine. When it has
dropped to 90% of its original value the engine will be down on power and would
benefit from a rebuild. When it’s dropped to 80% it really needs rebuilt! Using the
table below will help you determine monitor the condition of your top end.
Engine is Fresh
Measured Value
Engine Down on Power
Measured Value * 0.9
Engine NEEDS Rebuilt
Measured Value * 0.8
Procedure for Compression Testing
1. Shut off the fuel petcock.
2. Install the compression gauge into the spark plug hole.
3. Hold the throttle to wide open, and kick repeatedly (approximately 20 times)
or until the gauge reading does not increase in value with each kick.
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