Go easy on me now!  I have a old, rebuilt recently Rochester Carb. It seems to perform great after It comes off the initial opening of primaries. At idol, starting out in first gear, or after a slow down in any gear. The beginning of the throttle opening has a slight flat spot or hesitation. Am I to lean on air screws or is there a internal problem with carb? After it begins to accelerate, 12-1500 RPM it runs GREAT. Secondaries SLAM in and is seemless in performance. Do I live with it or try to remedy the flaw?  THANKS for the input.  CARLISLE is comming so I need to make a decision so I can look for something else if need be, new or used.  I am aware of the qualities of EDELBROCK, but would like to stay with OEM for gas economy and the originality.  Mark

It's been a long time since I worked on an old Carb but I do recall back in the day this was sometimes  caused by the accelerator pump. There was a little leather type cup it there and if it failed you'd get a flat spot on initial acceleration. That pump gives a little squirt of gas at intitial acceleration. If it doesn't you gat a lag, or flat spot. I don't know how to describe it but it will be on top of the carb probably on the bowl section. It's possible the bowl isn't filling all the way due to a stuck float.
This all from memory. Like I said it's been a long time.
But before I'd do anything drastic I'd check the Idle adjustment. Idle adjustment might also cause it and so can a faulty advance mechanism
BillinNashville2010-07-07 06:42:54

I agree.  I would also suspect the accelerator pump linkage.  Sometimes there are two holes to choose from, and there are adjustments on the rod.

Larry