I use and sell the Mikuni VM 36mm carb, which I use on my Savage. It has both the UFO and Dial-a-jet devices installed, but the carb can be used quite effectively without the devices. I am a tinkerer ... always playing with the thing to see what I can do to improve power & responsiveness.
A stock carb can be rejetted, with or without a filter change like a K&N type item, and you will improve the power and responsiveness noticeably. The cost for a pilot and main jet is only about $3 each, and the white spacer mod is free if you do it yourself. Depending on the filter you may choose, the entire thing can be done for $25-60.
Of course, any time you modify an engine to make more power, you may loose a little in the mpg area ... but not always. My engine is modified a fair amount, making up to 45 hp on one of the last tests I did with it before beginning the current rebuild. When my Savage was stock the milage was 52 mpg ... recent milage was 48 mpg. That is the average for basic riding. Really hard riding yielded as low as 40 mpg (wide open all the time doing test runs and such), while cruising the hiway would go up to 50 mpg.
Switching to a Mikuni VM carb with stock or pod filter and HD or Supertrapp muffler for ex. will produce a big boost in power and responsiveness, with little loss in milage for easy riding.
This is assuming that the final jetting/fine tuning is done well so that the fuel/air mixture is proper. Too lean or rich and it can create problems and loss of milage.
If you have an interest in the UFO or Dial-a-jet you can check out the tech info on them at
www.thunderproducts.com. I am an authorized dealer for them as well as Sudco, Barnett and Nonlinear Engineering.
I discount prices by 10% for members of this website on all products I have available.