Honda BF20A-BF25A, BF25D-BF30D Outboard Motors Shop Manual., Page 115Get this manual
HONDA BFSOAmS5A
6VALVE SEAT RECONDITIONING
1) Thoroughly clean the combustion chambers and valve seats
t remove carbon depositsApply light coat of Prussian Blue compound or erasable felt-tipped marker ink to the valve faces2) Insert the valves, and then lift them and snap them closed against their seats several timesBe sure the valve does not rotate on the seatThe transferee! marking compound will show any area of the seat that is not concentricNOTE Follow Valve Seat Cutter Manufacturer's Instructions
[I VALVE FACE
3) Using 45O cutter, remove enough material produce a
smooth and concentric seatTurn the cutter clockwise, never counterclockwiseContinue turn the cutter as you lift it from the valve seat