Small hobby engines with masses less than 1 kg are attractive for use in low cost unmanned air vehicles (UAVs) because they are mass produced and inexpensive, however very little information about their performance is available in the scientific literature. This thesis describes the development of a dynamometer system suitable for measuring the power output and efficiency of these small engines and presents detailed performance measurements for a particular engine with a mass of 150 grams that could be suitable for powering a low-cost UAV. The performance of the engine was found to improve considerably by controlling the fuel-air mixture. The objective is to use the dynamometer system to collect data that provides insight into the processes/loss mechanisms governing small engine performance so that it may be improved and to develop scaling laws for the performance of engines in the 20 g to 1 kg range that may be used by designers of low-cost UAVs.