1987-2009 Yamaha ATV YFM350X Warrior Raptor Service Manual, Page 106Get this manual
ENGINE DISASSEMBLY
5Check: -Valve sealing Leakage at valve seat Inspect the valve face, valve seat and valve seat widthRefer to "INSPECTION AND REPAIR VALVE SEAT"NOTE: Before removing the internal parts (valve, valve spring, valve seat etc.l of the cylinder head, the valve sealing should be checked
Valve seat checking steps: Pour clean solvent CD into the intake and exhaust ports Check the valve seatingThere should be no leakage at the valve seat