1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 91Get this manual
CHARGINGSTARTING SYSTEM
Cleaning and Inspection
1Clean all motor parts2Check pinion teeth for chips, cracks or excessive wear3Replace the drive clutch spring andor collar, if tension is not adequate, or if wear is excessive4Check that the brush holder is not damaged or is not holding the brushes against the commutator5Replace brushes that are pitted or worn to less than 14 in(6.4 mm) in lengthRefer to "BRUSH REPLACEMENT", following
14 in(6.3 mm)