Yamaha Marine Outboards F4A/F4 Factory Service Manual, Page 164Get this manual
POWR ROCKER ARM AND VALVES
3 The valve seat is too narrow and is near the valve margin
Valve seat cutter set First: cutter Use Second: 45 cutter
Desired result To achieve centred valve seat with the proper with
4 The valve seat is too narrow and is near the bottom edge of the valve face
Valve seat cutter set First: 60 cutter Use Second: 45 cutter