340 carb size

thanks guys,I have put a lighter spring in the vac diaphram so hope this will help It had a black spring in it.compression is 180 psi at cranking so that seems to be plenty and we think about 2200 stall. Cam is set 0 degs.the graphs say 600-640 cfm.was looking at demon carbs are they any good?I was thinking maybe a 625 road demon,what rare tour thoughts