So after that Carburettor service, sparking plugs cleaning and petrol tuning, I have calculated the mileage of my Khyber.
Filled up the petrol tank upto the neck, and turned the odometer to 0000. Drove 142 Km, went to the same pump and filled the tank to its neck again. 15 Liters of petrol was poured in.
142/15 = 9.4 Km/L
Very very bad for 1000cc car. The car was driven on Islamabad roads, no traffic congestion conditions.