Pollutants are harmful to human and other living beings on the earth. Thus emission reduction plays a very important role in the survival of living beings. Hydrocarbons (HC), Carbon monoxide (CO), Nitrogen oxides (NOx) are the emission constituents which results in smog, respiratory problems in human beings, acid rain respectively. Hence, Indian government has taken necessary steps to reduce these emissions and imposed various level of norms like BSI, BSII and BSIII on 2/3 wheeler industries in the year 2000, 2005 and 2010 respectively. Presently in India, BSII is in force and from October 2010 BSIII will be introduced. BSIII 3 wheeler norm, the CO emission level is reduced by 44.4% and HC+NOx is reduced by 37.5%.The main objective of this work is to reduce the emissions like HC, which is due to unburnt fuels, NOx, which is due to high engine pressures and temperatures and CO, which is a byproduct of incomplete combustion. A serious attempt has been made to comply with the stringent BSIII norm without any compromises in engine performance levels.The following methodologies are well thought for reducing the stringent emission levels in Gasoline/Liquefied Petroleum Gas (LPG)/Compressed Natural Gas (CNG)-based 2-stroke and 4-stroke 3-wheeler engines. Since NOx generation is basically temperature dependent, the strategies like retarding the ignition timing, reducing the engine compression ratio, AFR (air-to-fuel ratio) optimizations are used to reduce the engine temperature and hence to control NOx emissions. As CO is a byproduct of incomplete combustion, the strategies like secondary air injection (SAI), optimization of catalytic converter (catcon) parameters like volume, structure, cell density, noble metal loading and wash coats, will burn the unburnt gases and hence reduces the CO.The unburnt fuel, i.e., HC is controlled by strategies like improving the combustion efficiency by optimal engine, SAI and catcon designs. BSIII norms are met with the above strategies by keeping minimal changes in engine with optimal cost impact.