Yamaha Outboard F15A F9.9C, FT9.9D F15 Service Manual, Page 150Get this manual
INSP ADJ
GENERAL
6Measure: Compression pressure Too high Inspect the cylinder head, valve surfaces and piston crown for carbon depositsToo low Squirt few drops of oil into the affected cylinder and measure againRefer to the following tableCompression pressure: 961 kPa (9.8 Kgcm2, 139.4 psi)