Stumble off idle on 450

I have a 1957 450 gas. The problem I'm having is when you crack the throttle from idle to WOT it will spit and sputter at first and then take off.
I had the head off and put all new valves in cut the seats and milled the head .010.So far I have checked the timing,checked the points,set the float in the carb,checked the valve lash and still it runs poorly.
Any ideas?
Thank you

KEV

I've never been into a carb such as yours, but most have what is called a "cross-over" circuit.

Sometimes this is nothing more that a "slit" or sometimes a springloaded wafer "valve" in the throttle plate.

In other applications, it is another complete circuit entirely in the carbureator throat and only 'feeds' at those times when the throttle is just off idle.

At any rate, it sure sounds like that "stumble" is carb related, tho.

Tryin' to help,

Allan