Abstract The main drawbacks of two stroke (2S) engines consist in poor engine efficiency and high level of pollutant emissions. The contemporary opening of transfer and exhaust ports during the scavenging process causes the short circuit of fresh air-fuel mixture in case of indirect injection or carbureted engines. Despite the intrinsic strengths such as high power density, simplicity, compactness, lightweight and low production costs, 2S engines have been substituted by four stroke (4S) engines in many applications. Direct injection represents an effective solution to reduce the short circuit of fuel in 2S engines. Usually it is carried out by adopting high-pressure systems but the related increase of complexity and costs is inevitable. In order to maintain the intrinsic simplicity of a 2S engine, the most suitable solution is represented by a Low Pressure Direct Injection (LPDI) system. 2S LPDI engines are characterized by the presence of one or two injectors, working at 5 bar, installed on the cylinder wall. Previous works of the authors have shown the effectiveness of an LPDI system applied to a 300cc single cylinder engine in underpowered version with different ports timing and exhaust system with respect to the full power configuration. In the present paper, the authors show the fine-tuning of a 2S engine in full power configuration provided with two injectors installed on the cylinder and directed towards the exhaust port; the injector nozzles were located above the scavenge ports in order to guarantee the maximum interaction between injected fuel and inlet air flow. The engine has been deeply tested and analyzed at the test bench. Particular attention was paid to definition of the optimal injection timing in order to guarantee the best compromise between performance, efficiency and emissions. The experimental setup and the calibration methodology are discussed in detail. The results show the advantages of the LPDI system in terms of increased engine efficiency and emissions reduction with respect to the original carbureted engine maintaining the same level of performance.