Mercury Force 9.9, 15HP Outboards Service Manual, Page 63Get this manual

Mercury Force 9.9, 15HP Outboards Service Manual, Page 63

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6 Remove spark plugs from power head I"
7 Crank engineOBSERVE POSSIBLE CAUSE

Weakyellowish or red spark
Poor groundsDamaged or worn high tension leadMalfunctioning stop switch