A Design of experiments methodology was carried out to investigate the effects of compression ratio, cylinder head material, and fuel composition on the engine speed, fuel consumption, warm-up time, and emissions of a carbureted single cylinder air-cooled spark ignited engine. The work presented here is aimed at finding out the sensitivity of engine responses, as well as the optimal combination among the aforementioned parameters. To accomplish this task two cylinder heads, one made of aluminum and the second one of cast iron, were manufactured; an antechamber-type adapter for the spark plug to modify the combustion chamber volume was used. Ethanol/gasoline blends containing 10 and 20 volume percent ethanol were prepared. Engine performance was evaluated based on the changes in engine speed at idle conditions. The concentrations of CO2, CO, and HC in the exhaust were recorded. The test results show that the higher engine speed, lower HC, and lower CO2 take place for the aluminum cylinder head, higher level compression ratio, and 10 percent ethanol blend combination. The lower fuel consumption corresponds with the aluminum cylinder head, higher level compression ratio, and 20 percent ethanol blend case. The shortest warm-up time is achieved with the cast iron cylinder head, the higher compression ratio, using 10 percent ethanol blend. In general, it is also concluded that CO and HC emissions decrease with the increase of the ethanol content in the fuel blend. The results indicate that cylinder head material affects engine behavior, but less than expected. Among the three factors varied within this work, and limited by their level values, the compression ratio is the most influencing parameter affecting the engine performance at idle conditions.