1- I could not find any adjustment screw on its carburettor as it is different from conventional carburettors being used in other local motorbikes in Pakistan. I will take it to authorized Suzuki mechanic on weekend, Insha Allah.
2- I tried doing this experiment three times while coming to office this morning. While riding at a constant speed of 60 km/h, I turned off fuel cork and noted the distance covered before the engine started to stall. Here are the findings:
[TABLE="class: grid, width: 500, align: center"]
<tbody>[TR]
[TD]Iteration[/TD]
[TD]Mileage (km)[/TD]
[/TR]
[TR]
[TD]1[/TD]
[TD]1.0[/TD]
[/TR]
[TR]
[TD]2[/TD]
[TD]1.3[/TD]
[/TR]
[TR]
[TD]3[/TD]
[TD]1.3[/TD]
[/TR]
</tbody>[/TABLE]
I got a lesser mileage in first run because I had to slow down twice for speed-breakers; in the consequent runs, I drove it at a constant speed of 60 km/h on a straight road without having to slow down. Since I got 1.3 km twice on a constant-speed run, I would assume my bike does 1.3 km on one full carburettor.
Performing reverse calculation from the fuel-average reading I recently got (37.5 km/L), a fully filled carburettor contains approximately (1.3/37.5 = ) 0.035 L (or 35 mL) of fuel. Yesterday I got (700/109.6 = ) 6.39L of fuel from Shell, and according to these calculations it would cover a mere (6.38 X 1.3/0.035 = ) 237.34 km only - bad! 
It means, bike should do more on one filled carburettor. Agree?