A secondary air supply passage joins a reed valve chamber provided on a cylinder head cover and an exhaust gas port. The secondary air supply passage includes three aligned passages formed in a cylinder head, a cam holder and a cylinder head cover. The secondary air supply passage is formed perpendicular to a cylinder head gasket. One end of the secondary air supply passage opens to a secondary exhaust gas air induction part, formed integrally with a core of the exhaust port, during casting of the cylinder head.
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