The article presents the possibilities of improvements the crankcase delivery ratio in small two-stroke engines by modification of the inlet system by means of an additional side volume connected with the inlet pipe. The results of calculations from numerical simulation of gas physical parameters, taking into account thermodynamic phenomena in the inlet system and crankcase, are closed to those obtained during experiments. Influence of different geometrical parameters of the inlet system on the crankcase delivery ratio is considered. The application of such system increases engine delivery ratio and improves air-fuel ratio over the whole range of engine speed, especially with part-throttle openings and higher engine rotational speed. Simulation and experimental variations of pressure and delivery ratio for various systems have been presented. Good correlation between theory and experiment makes possible a selection of this system at the early stage of design. A simple system can be applied particularly in small motorcycles, boat engines and agriculture engines. The enclosed figures show a schematic diagram of the system taken under consideration and comparison of engine delivery ratio with classic intake system and volume intake system.