2007-2009 Yamaha F15/F20 Outboard Service Manual, Page 16Get this manual
GEN INFO
General information
Checking the outboard motor mounting height
CAUTION:
A protective covering is installed on the intake silencer when the outboard motor is shipped from the factory and must be removed before starting the engine for the first time
1Check that the anti-cavitation plate is between the bottom of the boat and maximum of 25 mm (1 in) below itIf the mounting height is too high, cavitation will occur and propulsion will be reducedAlso, the engine speed will increase abnormally and cause the engine to overheatIf the mounting height is too low, water resistance will increase and reduce engine efficiency
Checking the fuel system