Optical measurement techniques were successfully appointed in four stroke combustion diagnostics because of low interaction and high efficiency. In the field of high speed small engines only less experience exists concerning optical measurement. These engines require sophisticated measurement techniques concerning available space and resolution.Numerous investigations with different measurement techniques to analyze the combustion will be presented in this paper. Engine operation, combustion phenomenons and the limits of some techniques are shown by means of concrete examples. The use of fibre optic endoscopes allows the analysis of flame propagation. Furthermore it is possible to locate glow ignition. By means of spectroscopic measurement the mixture preparation and burning temperature curves could be analyzed by adding special reactants to the fuel.