1998-2006 Yamaha F20/F25 Outboards Service Manual, Page 261Get this manual
! SHIMMING (EXCEPT FOR USA AND CANADA)
Example: If is "16.25 mm" and "F" is "+4", then: T1= 17.5 mm(+4)10016.25 mm17.5 mm0.0416.25 mm1.29 mm (0.051 in) If is "16.26 mm" and "F" is "-3", then: T117.5 mm(-3)10016.26 mm17.5 mm0.0316.26 mm1.21 mm (0.048 in) 3Select: Forward gear shim Calculated numeral More than 1.00 1.10 1.20 1.30 1.40 or less than 1.10 1.20 1.30 1.40 1.50 Shim size to use 1.0 1.1 1.2 1.3 1.4