I've never truly and accurately computed my MPG, but have learned that when I hit 180 miles I'd better start looking for a gas station as I've had to switch to reserve on a couple of occasions when I went over 190 miles. I've done the .22 mod/low-buck exhaust mod and my fuel screw's out about 2-1/4 turns. That may cause it to use more gas, but it runs good and never pops anymore, so I'm leaving it be. I'm about your size and think I get about 40mpg.
I'm only theorizing that if I rode 72 miles instead of 60 miles and that if I rode it all at 70mph instead of my usual 60mph or so, my gas mileage might be comparable to what you're getting? Engine would be running harder and a lot more wind resistance.