Abstract: An exhaust gas recycling system for reducing nitrogen oxides discharged into the atmosphere by internal combustion engines, comprises an exhaust manifold having a baffle therein and a bypass pipe leading from the exhaust manifold to the air intake of the carburetor for returning a portion of the exhaust gases to the inlet of the carburetor in direct dependence upon the vacuum in the inlet to the carburetor, thus automatically recycling a substantial portion of the exhaust gases during those periods of operation when such recycling is desired, i.e., during acceleration and normal operation, when the vacuum at the carburetor inlet is high, and recycling only a minimal quantity of exhaust gases during those periods of operation when such recycling is not desired, i.e., during cranking, idling, deceleration and high load operation, when vacuum in the carburetor air intake is low.