Honda BF9.9A-BF15A Outboard Motors Shop Manual., Page 74Get this manual
HONDA BF9.9A-BFISA
dVALVE SEAT INSPECTION AND RECONDITIONING
1) Thoroughly clean the combustion chambers and valve seats to remove carbon depositsApply light coat of Prussian Blue 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 transferred marking compound will show any area of the seat that is not concentric
3) Using cutter, remove enough material to produce a
smooth and concentric seatTurn the cutter clockwise, never counterclockwiseContinue to turn the cutter as you lift it from the valve seat