I think your gas consumption is way to high for that little engine. By comparison, here is some of my vehicles consumption;
3.3 truck - 20 mpg = 8 km per liter
3.0 van - 22 mpg = 9 km per liter
2.0 car - 35 mpg = 14 km per liter

It would be a good idea to get your car tuned-up by a trustworthy mechanic. Not all casa/dealer mechanic is good and not all run-down mechanic is bad, its how they work and how long they guarantee their work.