I have found the older 2-stroke trail machines I ride get the following miles per gallon (mpg):
1991 Polaris Indy Trail Deluxe, 488cc fan = 12 mpg without pulling a load; 8 mpg while pulling a load (350 lbs)
1994 Polaris Indy Classic, 488 liquid = 9 mpg without pulling a load; never pulled a load with it
1996 Polaris Indy Lite GT, 339 cc fan = 16 mpg; 12 mpg pulling a light load (150 lbs)
1998 Ski-Doo Skandic 377 cc fan = 15 mpg; 10 mpg pulling a load (350 lbs)
With my machines the mpg decreases from 25-33% (% mpg decrease = 1 - loaded mpg/unloaded mpg x 100) when pulling a reasonable load.
The liquid-cooled machine has the most brute power, but gets the worst mileage, which is an obvious trade-off.
Anyone have any mpg comparisons they want to share?