1980 Johnson 4HP Service Manual, Page 26Get this manual
If leakage persists, drill 18 inch (3.2 hole through the center of the plug to depth of not than 116 inch (2 below its surfaceWith punch, carefully out the plug See Figure 3-141nspect and clean the casting contact areaIfnicks, scratches, out-of-round condition exist, the casting will have to replaced If casting opening is normal, apply bead of Adhesive to the outer edge of new core plugPlace new core plug in casting, convex side upFlatten to tight fit with flat end punch and mallet, and check for leakage LEAD SHOTS If leakage occurs at lead shot these corrective measures: follow Figure 3-16Removing Lead Shot
If leakage is slight, smart tap with hammer in the center of the lead shot will normally correct this conditionSee Figure 3-15
FUEL TANK Inspect the filler and gasket for wear, damage, leakage; replace if necessaryRemove shut-off valvegum and varnish deposits washing in Engine CleanerApply drop of part number 200763 Gasoila to threads at shut-off valve installation to fuel tankInspect the fuel tank for leakageIf leakage occurs, replace tankdFlush tank with clear gasoline least solvent at