I have a 2000 zr600efi and the gas mileage is between 5 to 7 miles a gallon. It is bone stock. It bogs out of the hole sometimes and I found out my cam bushings and bolts were worn out. I've heard that arctic-cat doesn't really have that much faith in the efi so they run in on the rich side. So I was told you can fine tune with an adjustable fuel regulator. I want to stay away from aftermarket chips. Thanks for any information.