I'm running a 750 Speed Demon right now. I love it, but they are kinda hard to get tuned right if you didn't get the correct carb for the job. We had to do a few modifications to my carb to get it all dialed in. Before getting one of these carbs it's good to call Barry Grant Tech and tell them about what setup you plan on running mainly your cam specs and they will hopefully give you the correct carb to run.
My cam had a little to much duration for the speed demon and we had to basically turn it into a Mighty Demon to get it tuned right. It's nothing that I wasn't prepared for because I've read alot about the Demon's after I got mine and new what to expect. Once it's tuned it ran perfect, it's a very good carb and looks great too.