The engine in our SNJ (AT-6) with 1340-AN-1 would stumble and cough immediately if subjected to the slightest negative G while, say, performing a nice round loop.
All these years I may have misunderstood how the carb works, but my understanding is that the float controls the flow of fuel into the bowl from the supply line, not into the engine via the discharge line and venturi. That seems to be what figure 23 on page 16 in the PDF shows, too.
The throttle really controls air not fuel, of course, and that air sucks the fuel into the venturi--the more air (suction) the more fuel is pulled into the engine.
Stop the flow of fuel into the carb and no matter how hard it sucks the engine won't get any. Since we're only talking about the fuel in the bowl, a very small amount, the engine will quit almost immediately if the float stops the fuel coming into the engine.
I could be wrong about all this, but from experience I know I'm right that the engine will cough and sputter immediately, regardless of the mechanism, not after 30 seconds or whatever.
Get tech support for your Lockheed Vega here.