I also notice that, but i worry that when i bring the throttle down while maintaining the same RPM i am causing it to run lean. Also, where is the clip on your carb needle set? Mine seems to be running a little lean with the clip at the second notch from the top.2-strokes are peaky - I often notice that I'm holding throttle way too far open for the speed I'm going and can roll it back quite a bit and still go that same speed
however, my best mileage happens at about 25mph on level ground - I get way over 100mpg when I can do that