I'm not sure I agree that a k5 should have better gas mileage than a 250. I ride both and they are both jetted right. I often take turns with them and the 500 is always drinking faster. The 500's piston is basically twice the piston right? I would say that jetting and float adjustment will help out, but saying the 250 drinks more fuel would be like saying a big block chevy should have the same gas milage as a small block or even an in-line 6 cylinder. Maybe you guys are getting older and heading back to the truck sooner for breaktime. Maybe someone should put these theories to a test. Milage test on the same trail or track.
i have a 454 in my 98 chev truck with 4.10 gearing, i get about 13 to 14 mpg. my father has a 2007 dodge 5.7l (350 ci) "hemi" (even though it is a wedge head...) geared 3.43 getting the same fuel milage. i can tow a 28' covered trailer filled with bikes and a 3500 lbs camper, weight totaling about 9000lbs. i get about 10 mpg wi this set up. my father tows a 3000lbs trailer and gets 7mpg. just something to think about.
a yz125 has a 38mm carb, a stock k5 has a 39mm carb. my 99 yz runs dry long before my k5, but also keep in mind the yz's tank is smaller.
