39mpg on a 750!!
I reckon you guys bikes are using too much fuel. My 900SS would do 120 - 130 miles before the light would come on. I could run it to 150 before refilling no problem and I reckon it would run to near 180 miles to empty. Normal consumption was 10 miles/litre = 45.5mpg but I'd had as much as 55mpg on a run to the West of Scotland and back and as little as 35mpg on a track day.
The ST4s which has replaced it, surprisingly uses about the same amount of fuel on a day to day basis but on a recent fairly sedate (60-70) run from Glencoe to Tyndrum via Inverary managed an astonishing 63mpg.
I think that most jet kits for the SS are set up on the rich side. On the SS I found that even with an open airbox and a race can it didn't need larger than the 140 main jet and that the Factory Pro needles were happy on the middle notch. That was with the float height set to the Factory Pro recommendation of 14mm.
Also the carb models are prone to worn emulsion tubes and sticking choke assemblies none of which help the fuel consumption.