Specifications

34
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
Example
110 psi 110 psi * 0.9 = 99 psi 110 psi * 0.8 = 88 psi
Your Values
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.