In many rotary engines, over 10% of the fuel passes through the engine unused. This loss makes exhaust cleanup difficult and also represents a serious penalty in fuel economy. The major hydrocarbon sources were found to be apex seal leakage, cold wall zone effects, residuals and surface-to-volume ratio which included rotor surface quench and chamber surface quench. Lesser hydrocarbon sources were crevice volume, and effects attributable to spark plug, ignition system, turbulence, intake mixture and lubricant on the combustion chamber walls. Through various engine modifications we were able to cut base engine hydrocarbons about 55%.