1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 68Get this manual

1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 68

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1 Connect timing light to no1 (top) spark plug lead2 Shift engine into neutral3 Holding throttle arm at idle position, crank engine with starter motor and adjust idle timing screw to align degrees BTD