Abstract: An intake manifold structure for a multi-cylinder engine having first and second independent mixture generators such as carburetors and first and second intake manifolds communicating the mixture generators to respective plural cylinders. A control gas passage and a treating gas passage are provided for introducing a control gas such as return flow exhaust gas, an additional pulse of air or the like, and a treating gas such as crankcase blow-by gas to the manifolds. The control gas passage is arranged to open into the interiors of respective diverging portions of the intake manifolds. The treating gas passage is arranged to open to the interiors of any other portions, avoiding the diverging portions, of the intake manifolds.

Abstract: An internal combustion piston engine employs a main combustion chamber supplied with a lean combustible mixture through a main intake passage and an auxiliary combustion chamber supplied with a rich combustible mixture through an auxiliary intake passage. The auxiliary combustion chamber has a spark plug associated therewith, and a torch nozzle defined by a slot having its major axis extending along the principal axis of the engine cylinder.