A timing controlled auto-ignition named “AR combustion” could improve irregular combustion in the part load operation of conventional two-stroke engines. Our previous papers have suggested its idea and the drastic improvements in fuel consumption and HC emission proven through a bench experiments. This time, from a concept that improvements of a two-stroke engine should be done maintaining its original advantages, an AR combustion engine was developed by using a simple exhaust valve and maintaining engine's original power output. This engine was mounted on a motorcycle and experimented in the “Dakar rally”. As the results, good fuel economies exceeding a four-stroke rally model, excellent driveability and durability were proven, because of the improvement in the combustion and engine's potential for the downsizing. The AR combustion engine, consequently, has good prospects for the practical use.