Small power generators (up to 5 kW) with a dual-fuel function rely on the use of fuels with standardized quality parameters. The use of gaseous and liquid biofuels, produced by the prosumers themselves, to power the engines of these generators poses the problem of their impact on the operation of the fuel system and on exhaust gas emissions. The goal of this study was to indicate the environmental effects of adapting the internal combustion engine of a 2 kW multi-fuel generator to burn gaseous and liquid biofuels produced by the prosumer. Exhaust emission tests were carried out for the combustion of biogas, methanol, natural gas (methane) and conventional fuel. Forms of propellants that were generated at laboratory scale were used during the tests. Anaerobic organic waste management technologies were used in the tests. Biogas and biomethanol were generated for the tests. A modified SI generator fuel system: pressure reduction and fuel pre-conditioning, was tested burning gasoline, methanol, biogas and natural gas with 98% methane content. Exhaust gas emission tests in three operating states (idle, 50% load, 100% load) indicated CO2, CO, NOx and HC emission levels. The feasibility of using renewable fuels in a low-power generator was demonstrated, as well as the correct operation of the author’s system for supplying the generator with gaseous fuels. In the case of bioethanol, better complete combustion of the fuel was achieved than with gasoline, which was characterized by, among other things, 20% lower carbon monoxide emissions at full load. NOx emissions from the combustion of bioethanol compared to gasoline were 1.75 times lower at full load, and HC emissions were almost twice as low. In the case of biogas, there were significant carbon dioxide emissions due to the high carbon dioxide content of the fuel (40%). The other emission results for biogas were not significantly different from those from natural gas combustion.