This paper describes the strategies to improve fuel efficiency and reduce CO2 emissions for the three wheeler vehicle fueled with auto CNGIn today's scenario, it is very much important that the vehicle should have high fuel efficiency, where fuel economy is USP i.e. Unique selling features.The improvement in fuel efficiency will lead to reduce CO2 emission. In India, CNG is abundantly available and without treatment it can be used for vehicle application.This was achieved by redesigning gear ratios, vehicle fuel system and engine intake system. The main aim was to have vehicle should run in all the time in low engine SFC band i.e. Specific fuel consumption After several technical calculations and then actual physical testing, improvement confirmed on 5 proto vehicles in R&D was 23 % in City and IDC and 22 % on Highway respectively.The power found improved by 2 %.CO2 and other emission components i.e. CO, HC, and NOx found to reduce by 18-32 %.