1991 Yamaha Outboard Factory Service Manual 9.9 and 15 HP, Page 7Get this manual
GENERAL INFORMATION OUTBOARD MOTOR IDENTIFICATION
Engine serial number
SPECIAL TOOLS
The proper special tools are necessary for complete and accurate tune-up and disassemblyUsing the correct special tool will help prevent damage caused by the use of improper tools or improvised techniquesFor tune-up
The engine serial number is stamped on the plate attached to the cylinder body