Yeap.. i also almost ran out of gas the other day.. prob around the 160 mark and filled 1.9 gal, damn on the teetering edge of empty
I'm testing out with the petcock in the opposite position, curved edge facing down and handle facing up to see if its just oriented wrong. The petcock actually has a small arrow pointing in the direction of the edge of the handle, so, we will see. i'll report back if it works and it will be another quirk to notate..
With regard to the larger tank, check out this thread for the possible:
http://www.chinariders.net/showthread.php?t=29875