100 miles?? Jeez, what rear ratio do you have? Our engines are a pretty close match and I have 3.91 rear gears. I get around 10 mpg around town and 12-14 highway (60-70 mph). That puts me around 150-200 miles per tank with a 25-50 mile reserve.
3:23 and that was changed from 3:73. I've never gotten good gas mileage and Im stumped why? I was thinking the large (750) carb was the issue, hence why I swapped to the 600. But swapping to the smaller carb slightly improved it. Thinking about it if Im really easy on the throttle I can get maybe 120miles and that leaves me with a quarter tank of gas, but I dont know how accurate my gauge is so I dont push it. At 60mph, Im turning 2800rpm, at 70mph Im turning 3500rpm. I only have a 26.4" tire on the rear. So if I could get a taller tire that might help some also.