Well first off, with twin 750's sitting atop your intake the MPG is about right, if you want better MPG I'd lose one of the carbs and stick a overtranny tranny in there like a 200-r4 or a 750R, either way you've got to get your rpm's down.
If you think your stall is too loose, take it out & call Kenny Ford or Tim Owens @ PTC. They can fix you right up.
Telephone: 256-383-6868
http://www.ptcrace.com/
Cp