Two-stroke cycle engines have excessive speed fluctuations and poor part-throttle fuel economy as a consequence of cyclic combustion variations and irregular combustion, leading to misfiring. This study is to identify the nature of cyclic variations and the regime of irregular combustion in order to understand the possible causes for this phenomena. Studies were carried out on a 150 cc two-stroke cycle S.I. engine. Statistical evaluations of peak pressure(Pmax) and indicated mean effective pressure (imep) were used to characterize cyclic variations and irregular combustion. A parametric study on the effect of air fuel ratios, spark timing, engine speed, spark plug locations, throttle setting, and cylinder head shape on cyclic variations were carried out. The study has identified the regimes of stable combustion, irregular combustion and misfiring. Cyclic variations and irregular combustion are largly dependent on throttle settings which are indirectly due to the residuals present in the cylinder. The factors which increase the combustion delay appear to have a major effect on cyclic variations.