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Cannot Find Compression Specs On Johnson 15HP

B

bobbyg

Member
I have a 2007 Johnson 15HP 4-Stroke with 130 & 120 PSI. This seems low, I thought it should be 150+. Cannot find actual stats. Motor idles well but will not run beyond half-throttle. Carbs have been through ultrasonic cleaning 3X. The motor sat for a long time and I worry that the rings and/or valves are the problem.
 
It is a SUZUKI motor.-----If it idles well there is no ring / valve issue.----I say it is running on just 1 cylinder.----Could be just a bad sparkplug.-----Remove top plug lead and see if it starts.-----Then try the same with bottom plug lead removed.
 
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