[Eddy K]

I am experiencing that same problem right now. I am no carburator expert but I do have a Holley book and have also talked to Jegs tech line about this.
From all I can find out, this is a common problem with 850 cfm double pumper Holleys with manual secondaries.
When you hit the throttle it creates a lean condition which in turn creates a stumble. You need a bigger shot of fuel to overcome this.
I have ordered a 50cc accelerator pump to see if that helps and you can also install bigger squirters. The stock size is about a 31 and the tech guy recommended 37's.
I am going to give this a try tomorrow and see how it works.
The only way to stop this or lessen it is to just experiment.
Actually, the best thing to do for on the street use is to get a carb. with vacuum secondaries.