I would say you should be expecting closer to 8 - 9 miles per gallon. There are many factors that can effect your milage, but I would suggest making sure you have the carbs jetted properly for the temperatures you are riding in. Having the right jetting will help maximize your milage.
I get about 10 mpg on my Zr 500 EFI under normal riding conditions.
I know Dano has a 700 RMK and I think he runs in around 9 - 10 mpg when he has the correct jets in for the temperature.
I have a 96 Zrt 600 and i dont know for sure but my milage sux,but from a toy i dont realy expect to get miles just smiles.but ya i would look at jets and belt,track system to,one bad boggy is like a flat tire.hope this helps n happy sledin.
I see this is a really old thread, but I have a 800 RMK Indy with the ultra-lite short track (black) and can't seem to get more than 5 mpg out of it. A buddy has the newer 800 with the long track (blue - '03 I think) and he says he gets twice that and he rides harder than I do but it does have the variable exhaust so maybe its apples & oranges. It also runs rough at low rpm which makes me think something is wrong but not sure where to start. Carb adjust? Timing adjust? I haven't worked on these thing much so please give details if you have any ideas.