Q: Mostly short journeys are done. Example 10litre of petrol would allow me to do 25 miles. Is that about right?
A: 25 miles for 10 litres of petrol! Are you sure someone isn't syphoning your tank? That works out at just over 11mpg!! Either you're driving it like a madman, or it's got a serious problem (more than just engine tuning-related, like a major petrol leak), or your maths is a bit off! Should do about 35+mpg town, 50+mpg on a run.