It is important to improve motorcycle engine performance at low and medium speed according to Chinese market.First,the influence of the intake port on engine performance is considered and three good intake ports are selected.Through stationary flow test,it is found that intake port with a smaller caliber and a longer passage will make a better characteristic curve at the low and medium speed.Secondly,the engine combustion is more important for improving the engine performance.Therefore the scheme of improving combustion system of motorcycle engine is put forward.The compression ratio can be increased after changing the shape of the piston top and cutting the height of the cylinder.At the same time,increasing the flakes of cylinder head and some circular fillisters milled on the skirt of piston for storage oil,and oil injection device are adapted to decreasing the temperature.All the measures can keep the engine from knocking and high temperature.Lastly,how to match the motorcycle engine with three-devices(air filter,carburetor and muffler) is also considered.Exchange tests are carrying on with different three-devices.Based on the above research,the right way to develop the correlative engines is pointed out.