I just found the site and saw this thread. I have one of the American Lifan bikes too. It is the older model GY2, but almost the same.
I have been getting about 70mpg. You need to remember the odo is in KM and I believe the specs are not perfect and a 100km to the gallon is probably close.
If you all what more info on these bikes look up
www.chinariders.net and do some research.
I have 4200 miles on mine and lots of smiles. Also recomment Brian at motoxtreme.net also as he is an upstanding seller.
Allen