1963-1973 Mercruiser all Engines and Drives Service Manual Books 1 and 2, Page 233Get this manual

1963-1973 Mercruiser all Engines and Drives Service Manual Books 1 and 2, Page 233

SPARK PLUG DIAGNOSIS (CONTINUED) PLUG CONDITIONS FACTORS CAUSING THIS CONDITION CORRECTIVE AC TION Oil or Corban Fouling
mixture or (4) plug too "hot" for operat ing speeds and loads Plugs should be every 100 hours regapped Rapid Electrode Wear
Correct engine conditionInstall plugs to specified torqueUse new park ug seat gasket each time new or cleaned spark plug
is installedUselder" type lug if ondition ontinues to exi 1Replace with new spa rk plug Broken Upper Insu lator (Firing around
sh ell crimp under load cond iti ons ) Care less remova or insta Ilat ion of spark plug Broken Lower InsulatorFir ing Tip)
The couse is usually carelessness in regapping by either bend ing of centerwire to adjust the ga or permitting the gapping
tool to exert pressure aga inst the tip of the center electrode or insulator when bend ing he side electrode to ad ust the
go pFracture of breakage of lower nsulotor alsemay occur occasionally if the eng ne ha been perated under conditions causing
severe and prolonged detonat ion or pre- ign it ion Replace ith new spark plug Usecolder" type plug for the particular type