Abstract: A weak tumble flow fast combustion system is provided. An intake throat and an exhaust throat are provided on a cylinder head, a section of an intake duct close to the intake throat is a tumble guide duct, an axis of the tumble guide duct is arranged obliquely with respect to the bottom surface of the cylinder head, and an upper side surface of the tumble guide duct is a flowing-down guide surface arranged obliquely with respect to the bottom surface of the cylinder head, a lower side surface of the tumble guide duct is an arc-shaped guide surface recessed toward the bottom surface of the cylinder head, an eccentric chamfer is provided at the lower end of the intake throat, and the eccentric direction of the eccentric chamfer is offset along the direction connecting the center of the intake throat to the exhaust throat.