2005 Kawasaki STx-12F Jet Ski Factory Service Manual., Page 197Get this manual
ENGINE TOP END 6-29 Valves
If the seat width is too wide, make the 60 or 55 [A] grind described belowIf the seat width is within the specified range, lap the valve to the seat as described belowGrind the seat at 60 or 55 angle until the seat width is within the specified rangeTo make the 60 or 55 grind, fit 60 or 55 cutter into the holder, and slide it into the valve guideTurn the holder, while pressing down lightlyAfter making the 60 or 55 grind, return to the seat width measurement step aboveCorrect Width [B]