I've never had the that air leak problem you are describing, I'd take apart and rebuild your vertical reg if I were you. I take it is a Max-Flo vertical?
I think I can pull about 700-800 on my Impulse, although mine has a few ups in it, such as Voodoo derlin bolt, lightweight hammer, a nice hammer cap and a full freak kit. Impulses are known to be quite air hungry though.