1985 OMC 65, 100 and 155 HP Models Commercial Service Manual, PN 507450-D, Page 71Get this manual
Maximum Spark Advance Adjustment The characteristics of the ignition systems used on 100 and 155 models result in an automatic increase in spark advance over the basic setting as rpm increases from idle speed to approximately 5000 rpmFor this reason the most accurate setting is made when the motor is run over 5000 rpm Run the engine with the proper test wheelDo not run the engine with propeller or flushette for the adjustment100 Model 1Connect timing light to the No1 cylinder 2St art and run the engine to minimum of 5000 rpm in forward gear3The engine timing mark must align with mark on the flywheel gridRefer to the decal on the engine for maximum spark advance
4To adjust, stop the engine and loosen the timing adjustment screw nut Turn the adjustment screw in or out as necessary to correct the timingOne turn clockwise retards timing about 10and one turn counterclockwise advances timing about
105Tighten the nut, and recheck the timing adjustment155 Model 1Make initial adjustment of the adjustment screw Q) to 9-11 mm (3 8"-7 16") This is just an initial starting dimension2Connect timing light to the No1 cylinderStart and run the engine to minimum of 5000 rpm in forward gearObserve the degrees of advance indicated by the timing pointer with No1 cylinder timing grid on the flywheelStop the engine3Connect the timing light to No2 cylinderStart and run the engine to minimum of 5000 rpm in forward gearObserve the degrees of advance indicated by the timing pointer with No2 cylinder timing grid on the engineStop the engine