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

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SPARK PLUG DIAGNOSIS (CONTINUED) PLUG CONDITIONS
Plugs should be every 100 hours
regapped

Rapid Electrode Wear

Correct engine conditionInstall plugs to specified