1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 100Get this manual
TIMING, SYNCHRONIZINGADJUSTING
2DMT 2000 Digital Tachometer Multi-meter PN 91-854007A1
Checking Ignition Timing
NOTE: The ignition ECM unit electronically controls the ignition timing, therefore making the ignition timing non adjustableWhen initially running the outboard, use timing light to verify that the ignition timing falls within the timing ranges as described within the following testsIf the ignition timing does not stay within the timing ranges, refer to the Ignition Diagnostic Procedures tests in Section 2A1Connect timing light to no.1 spark plug lead2With outboard in water, start engine and allow to warm up3Set engine speed at idle speedVisually check the timing pointer to verify it is within the required timing range on the flywheelIf not, refer to Diagnostic Test Procedure in Section 2A30 5