I have 230E 1991 in 124W chassis. My 230E is running well till now, no smoke from muffler even I give a hard gas, but it has the problem in fuel economy, it's only 6 km/litre. The average speed/velocity in my town (Surabaya-Indonesia) is only 30 km/hour (a very crowded city).
Is it a normal fuel economy with my town condition ?. If it is not, what can I do to improve my 230E fuel economy ?
Can I fix it by myself ? If yes, would you please give me a brief explanation ?

Thank you