I had one mounted to the stock intake using a Weber 32/36 and I never got it to run really well. It ran ok, but I think the 32/36 is just too small a carb for the 250. I tried rebuilding it several times and never got much luck and finally got rid of it all several months ago.
However, I must say that at one time using a 3 speed, 3.07 gears, a tonneau cover, Stovebolt exhaust, and a reeeeeally light foot I was able to pull 18mpg on the highway.