New member with a question

Hello everyone I am new to this site and i really enjoy snowmobiling and working on snowmobiles and any sort of small engine im really big on vintage sleds. I have a 1974 John deere 300 2 up with electric start really nice old sled. and i just got a 1999 ski-doo Formula deluxe 500 fan so i could go on longer trail rides, its in excellent shape 6,000 miles with a brand new top end, im goin on a trail ride this weekend and was wondering how many gallons it wil hold and what kind of mpg it will get with steady riding out on the trail. If any of you could help me out with that thatd be awesome,

Thanks!