The improvement in engines efficiency and reduction of emissions is the permanent aim of engine industry in order to meet European standards regulation. To optimize small internal combustion engines it is necessary to improve the basic knowledge of thermo-fluid dynamic phenomena occurring during the combustion. This paper describes the combustion process in an optically accessible two-stroke spark-ignition engine used in a commercial 43 cm3 chainsaw. Two different feeding systems were tested: standard and CWI one.The engine head was modified in order to allow the visualization of the combustion using endoscopic system coupled with a high spatial resolution ICCD camera. Flame front propagation was evaluated through an image processing procedure. The image visualization and chemiluminence allowed to follow the combustion process from the spark ignition to the exhaust phase at high engine speed. All the optical data were correlated with engine parameters and exhaust emissions.The effect of the injection system on deposits formed by fuel accumulation and on the flame front propagation and unburned hydrocarbons emission was investigated. The use of CWI system allowed a fast and efficient injection and a reduction of unburned hydrocarbon emissions and specific fuel consumption. However it causes a worsening in combustion stability probably due to a less homogeneous distribution of the fuel as observed by optical means.