[Roo]

I?ve got a 2006 EC200 Which I?ve had about 6 months. My friend has a 1997 Eac200. Almost identical bike. If we ride together for about 40 miles, I need to put 8 litres of petrol in compared to his 4 1/2, to fill the tank.
I?ve spoken to a very helpful mechanic at GasGas UK who said it can?t be down to jetting or setup, as the bike runs great and that wouldn?t make that much difference. He said, float height. I?ve checked this and even reduced it a bit but I?m fairly sure it?s not that. There?s no evidence of fuel over flowing unless I tip the bike about 45 degrees. Seems to do what it should.
Bike runs fine at all points in the throttle. No sign of leaks. I?m stumped. Can 2 bikes that are essentially the same, be so different?
Any thoughts ?