Yar ye bottle wala tarika accurate nae hy avg k liye.
Y dont u go full tank to full tank, it may sound expensive but aap aik dafa full krwao (auto trip off k sath) ar next time say after 100 150 kms dubara full krwao. that would give u a better idea.
Afa carburetor opening is concerned, everyone has his own experience. Once when I went for its service, the mechanic at toyota walton suggested me not to do this he said "aik dafa carbi khul gya tau pehly jaisa nae rehta, aap cleaner mrwa lein ar jb tk guzara hota hy kren".
But on the other side, one of my colleague has an improved mileage after getting his carbi serviced from faislabad. So better take more opinions. And decide urself..