Must be getting air from somewhere???
You may have done this but check your seal between manifold and head, carbies and monifold. double check that the line to brake booster is not leaking. Also check the chokes on the dellautos are definatly closed as I think they can stick and even if the lever is all the way back it can still not be at zero(internal sticking)
Also are the plugs really wet if you take them out after running it. Is it backfiring?.
Thats all I can come up with of the top of my head.
Ash