Natural gasoline has been taken into consideration because the most promising opportunity fuel for its cleanliness and abundance. Due to this utilization of natural gas engines has grown to be vogue in some of countries, significantly extra in growing ones. However, to fulfill stringent emission regulations changes need to be delivered approximately in natural gasoline engine generation as forecasted reserves of herbal gasoline imply that it is going to be a prominent fuel in after time. Due to numerous effective properties that natural gas possesses viz. high-octane number, high C/H ratio, wide flammability limits, and so forth. It's miles greater fruitful to result in adjustments in existing engine technology to make NG a possible fuel compared to gasoline or diesel. NG engines can be operated in lean regime or stoichiometric conditions coupled with either high compression ratio or exhaust gas recirculation depending on the form of optimization i.e., Fuel economic or emission. This paper highlights effect of changes in injection and spark timings on overall performance, combustion and emission characteristics of an SI engine the usage of CNG or HCNG as fuel and necessity of an engine management system which needs to be hooked up to employ an ECU to carry out the adjustments in injection and spark timing. Advancement of injection and spark has its own advantages. Too much advancement of any of the two is not preferred either.