2000 Yamaha YFM400FWA(M) Factory Service workshop Manual, Page 133Get this manual
CYLINDER HEAD
CYLINDER HEAD INSPECTION 1.Eliminate: Carbon deposits (from the combustion chambers) Use rounded scraperNOTE: Do not use sharp instrument to avoid damaging or scratching: Spark plug threads Valve seats 2.Inspect: Cylinder head Scratchesdamage ReplaceCylinder head water jacket Mineral depositsrust Eliminate