Carb problems?

["Scott Hutchinson" <shutchin@netjets.com>]

When I accelerate from stop the car initially pull very strongly and
then begins to stumble.  If I then let off the gas and open it very
slowly I can "catch" it and get it to accelerate normally.  This is
happening anytime I open the throttle at mid rpm.  When I rebuilt the
carb the kit that I used did not include a new accelerator pump
diaphragm or spring could this be the problem?  If so which spring
should I use.  I'm running a holley 1948 with an F4B.
 
Thank in advance.
 
Scott