<p>This paper focuses on the effect of fuel-air ratio on the performance and cyclic variations of single cylinderhydrogen and gasoline fueled spark ignition engine. The hydrogen fueled engine was operated at the wide-openthrottle (WOT) condition, while the engine fuelled with gasoline was operated with conventional carburetor mode byvarying the throttle opening to vary equivalence ratio. All the experiments were conducted at a constant engine speedof 1600 rpm. The spark timing was set to minimum advance for best torque. As a result, it was found that there isabout 29% reduction in the maximum power output of the engine when operating with hydrogen. The equivalenceratio could have been varied in the range of 0.3 &lt;  &lt; 0.9 for hydrogen and of 0.8 &lt;  &lt; 1.3 for gasoline. In allcombustion periods, cyclic variations for hydrogen engine were much lower than that of gasoline engine. As aconsequence, it was found that the engine gave similar output at equivalence ratio of  = 1.1 for gasoline and  = 0.6for hydrogen. However the engine was operated more smoothly when fuelled with hydrogen.Keywords: Hydrogen, Gasoline, Performance, Cyclic variations.&nbsp;<br></p>