2006-2012 Honda TRX90 TRX90EX/X Service Manual, Page 116Get this manual
CYLINDER HEADVALVES Apply engine oil to new O-ring and install it into the groove of the carburetorInstall new gasket onto the intake manifold .a
Install and tighten the intake manifold mounting boltsInstall the followingExhaust system (page 2-7) Camshaft (page 721)
CAMSHAFT INSTALLATION