Mercury Mariner 4, 5 102CC Sail 1990 Outboard Service Shop Manual, Page 18Get this manual
Ignition Timing TOC Timing Mark Alignment
IMPORTANT: As this Ignition system utilizes electronic spark advanceno adjustment to ignition timing is possibleIf Ignition timing is not within specificationsrefer toTest Procedures" following to locate faully componenl(s)
IMPORTANT: IfTOC" mark on flywheel is nol In alignment with crankcase cover cylinder block split line, check for (and correct) one or more of the following possible causesaDial indicator has been improperly set up or misreadbFlywheel key is shearedcFlywheel is installed incorrectly
1Remove spark plug2i nstall dial indicator through spa rk ug opening in cylinder head
4Remove dial indicator and adaptors5 Insta ll spark plug and connect high tension spark plug lead