1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 63Get this manual
MAXIMUM TIMING 1Hold control arm so that maximum spark advance screw is against stop2Crank engine with starter motor and adjust maximum spark advance screw to align the specified BTDC timing mark on flywheel with timing pointer (due to the advance characteristic of this ignition system, this cranking speed adjustment will automatically be reduced by at an engine speed of 5000 RPM)Tighten locknut 2Install remaining spark plugs and high tension spark plug leads
aControl ArmMaximum Spark Advance ScrewLocknutThrottle ArmFull Throttle Stop ScrewLocknut