Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 33Get this manual
GENERAL INFORMATION
Cylinder Leakage Testing
NOTE: Cylinder leakage testing"', along with compression testing, can help the mechanic pinpoint the source of mechanical failure by gauging the amount of leakage in an engine cylinderRefer to the manufactures tester instructions for proper testing procedures
Courtesy of Snap-On-Tools
Cylinder Leakage Tester (Snap-On-Tools MT324) NOTE: Spark plug hole is 12 mm diameterUse Snap-On Tool MT26-18 adapter with valve core removed