1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 61Get this manual
4Reposition timing pointer if necessary, so that timing pointer is aligned with 0.491 in(12.47 mm) timing mark on flywheelRetighten attaching screws c a
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aTiming PointerTiming MarkAttaching Screws
aSet ScrewSynchronizing Screws
5Remove Dial Indicator, and reinstall spark plug and high tension spark plug lead of no1 (top) cylinder onlyCARBURETOR SYNCHRONIZATION 1Disconnect remote fuel line from engine2Connect remote control electrical harness to engine wiring harness3Remove throttle cable barrel from barrel retainer4Remove sound air box cover5Loosen screw from throttle cam follower6Loosen synchronizing screws7Look into throats of carburetors and make sure all throttle shutters are completely closedTighten synchronizing screws8Recheck throttle shutters necessary adjustmentsand make any