2004 SR Johnson 2 Stroke 9.9, 15, 25, 30 HP Outboards Service Manual, Page 173Get this manual
POWERHEAD GENERAL
GENERAL
Cylinder Compression Testing
Start and run outboard until it achieves operating temperature, then shut OFFRemove all spark plugs and disconnect the 5-pin power pack connectorAdvance throttle linkage to WOTInstall compression tester's hose attachment into spark plug hole (14 mm threads)While cranking outboard with starter, note maximum pressure reading on gaugeRepeat procedure for each cylinderReturn throttle to idle position and reconnect power pack connectorReplace spark plugs