Automotive emissions are the most important sources for air pollution in the city of Tehran. In order to control and reduce air pollution in this city, it is important to reduce vehicular exhaust emission. Patrol and pick-ups with Japanese originality have assembly line in Iran. These vehicles which are more or less popular in Tehran, originally have old design and not able to fulfill any new emission regulations. In this paper, Nissan engine Z24, combustion chamber has been modified, the orifice and main metering system in carburetor has been changed fundamentally and unleaded gasoline has been introduced to the engine. Reasonable reduction in exhaust emission has been measured on dynamometer under different loads and speeds. The new findings have been recommended to local manufacturer for mass production. The new Iranian Nissan patrol and pick-up will fulfill the moderate regulation mainly ECE 15-04.