8 Km/l isn't a bad average for a 18 years old carby engine. Don't listen to people claiming 14-15 Kpl from their rides.
My colleagues with Margalla, XE Corolla, Alto have all done many tricks. Still, they won't get anything beyond 8~10 mark.
Most of the juggaroo mechanics here don't understand carb. And if it is messed by one, you'll curse yourself for trying it....