1975 Johnson 4HP 4R75, 4W75 Outboards Service Manual, Page 20Get this manual
CORE PLUGS aIf leakage occurs at core plug area, smart tap with hammer and flat end punch in the center of the core plug will normally correct this conditionSee Figure 3-10If necessary, remove core plug to clean out slow speed orifice holesSee Figures 3-11 and 3-1B bIf leakage perSists, drill 18 inch hole through the center of the core plug to depth of not more than 116 inch below its surfaceWith punchcarefully pry out the core plugSee Figure 3-11cInspect and clean the casting contact areaIf nicKs, scratches, or an out-of-round condition existthe casting will have to be replacedIf casting opening is normal, apply bead of OMC Adhesive "M" to the outer edge of new core plugPlace new core plug in casting, convex side upFlatten to tight fit with flat end punch and hammer, and check for leakageLEAD SHOTS