2002/2003 Johnson SN/ST 2 Stroke 3.5, 6 8 HP Outboards Service Manual, PN 5005466, Page 136Get this manual
POWERHEAD SAFETY INFORMATION
SAFETY INFORMATION
Before working on any part of the outboard, first read the SAFETY section at the end of this manual
GENERAL
Cylinder Compression Testing
Start and run outboard until it achieves operating temperature, then shut OFFRemove spark plugs Advance throttle linkage to WOTInstall compression tester's hose attachment into spark plug holeWhile cranking outboard with starter, note maximum pressure reading on gaugeRepeat procedure for each cylinderReturn throttle to idle position Replace spark plug(s)Variation between cylinders on twin cylinder models should not exceed 15 psi (100 kPa)If engine shows variation greater than 15 psi (100k Pa), check for: damaged head gasket damaged pistons broken or stuck piston rings scored cylinder walls
WARNING