Bioethanol-gasoline blends represent for Otto-cycle engines a consolidated alternative in the attempts to reduce GHG emissions and to limit the use of fossil fuels. However, the use of alternative fuels can strongly influence the performance of engines. The purpose of this study is to analyse the output and the pollutant emissions of a four-stroke SI engine fuelled with 0%, 50% and 80% bioethanol-gasoline blends. Tests were performed on a 3-kW engine used in broad applications. No specific modifications were applied to the carburetion system in order to evaluate its fuel flexibility capabilities. The tests evidenced that the mixture tends to get lean with alcoholic fuels; the brake specific fuel consumption increased due to the lower LHV of bioethanol, while the highest brake thermal efficiency was obtained with E50. Minor torque and power reductions were recorded with the ethanol blends. The concentration of UHC decreased with E50 and E80 while NOx emissions reduced because of the lower combustion temperature due to the bioethanol cooling effect and the leaner mixture. In contrast, the concentration of CO increased because a poor homogenization of the charge and a lower combustion temperature had facilitated the formation of partial oxidation products. (C) 2016 Elsevier Ltd. All rights reserved.