1991 Yamaha Outboard Factory Service Manual 9.9 and 15 HP, Page 110Get this manual
Brushes 1Check wear on brushesIf they are worn more than 4.5 mm (0.08 in) they must be replacedBrush springs which are fatigued must also be replaced Starter pinion gear Check for pinion wear or damageCheck also ease of pinion movement (Sliding motion)
2Check whether the brush holders are bent or whether the contact surfaces are dirty, and recondition or clean as required3Check continuity between the insulated brush holder and groundIf there is continuity, the brush holder is grounded and should be replaced