This paper presents the experimental results of a Combined Heat and Power (CHP) prototype based on a SI V-twin internal combustion engine driving a synchronous generator. The paper presents the criteria that were used to select the combustion engine and the electrical generator for the prototype. The internal combustion engine has been adapted to be fuelled by natural gas or LPG, with the possibility of controlling the load in two ways, i.e. by changing the throttle position (quantitatively) and/or the value of the excess air ratio by changing the fuel dose at a constant throttle position (qualitatively). The applied method of control allows to improve the efficiency of the engine especially in the range of partial loads. The experimental tests were carried out at a constant speed of 1500 rpm. During the tests, the fuel consumption of the internal combustion engine, the composition of the exhaust gas at the outlet of the exhaust system, the electrical parameters of the synchronous generator and the temperature at selected locations of the CHP system instance were measured. According to the obtained results, there was a slight increase in the efficiency of electricity generation with the application of the developed method of control of the combustion engine. The maximum power generation efficiency for Natural Gas (NG) was higher compared to LPG by more than 2 percentage points.