1996 Johnson 115 HP V4 - Low Compression one hole

[Fr. Frank]

60 psi on one cylinder could easily be nothing more than stuck rings. However, head gaskets are relatively cheap, so pull the cylinder heads and visually inspect the cylinder walls and piston tops for scoring and carbon build-up. Examine the piston cap ridge (edge) for erosion or scoring. Turn the crank to move the pistons down in the cylinder and feel the cylinder walls for ridges or scratches.

If you find scratches or erosion, rebuild the powerhead.

If the piston and cylinder walls look and feel good, tilt the motor up and spray the inside of each cylinder with Quicksilver PowerTune. Don't be stingy with the stuff, use a whole can. Let it soak in overnight.

Reassemble the cylinder heads using new gaskets. Start the motor and let it run in gear at the dock or underway at 1500 to 2500 rpms for an hour or so, intermittently spraying more PowerTune into the air intakes. Don't shortcut this process.

After doing this, recheck the compression. If it was just stuck piston rings, your compression should now be improved.