Fuel never seems to be an issue for us as of late - with big CI engines we normally have to jet them down 1 or two steps both primary and secondary from stock - a good fuel pump and dual feed with the big needle and seats seems to solve the fuel flow issue -along with running the floats a little higher. I prefer the 800's on my 572 it was a huge difference on the Dyno. We do have one set of heavily modified that flow around 1000 CFM each - I have not tried them yet but they show promise