A carburetor does not really "squirt" the fuel into the intake air stream. Any "pressure" created by gravitational forces acting upon the fuel as it flows down the fuel line and into the carburetor will not increase the volume of fuel delivered into the intake charge unless your float is malfunctioning and the carburetor is flooding.
A carburetor works on the venturi effect.
Venturi effect - Wikipedia, the free encyclopedia
This is based on Bernoulli's principal.
Bernoulli's principle - Wikipedia, the free encyclopedia
The center portion of the carburetor throat is smaller than the entrance (air cleaner side) and the exit (manifold side). This area is called the venturi.
As the air passes through this narrowed section of the carburetor throat the air speed through it increases and the pressure decreases.
The float bowl of any carburetor must somehow be vented. This allows atmospheric pressure to exist inside the float bowl chamber. Atmospheric pressure is 14.7 PSI at sea level.
As stated above, during operation the ambient pressure decreases in the throat of a carburetor.
When this happens the atmospheric pressure present in the float chamber is higher than the ambient pressure present in the venturi and the fuel is pushed through the fuel jet, jet holder, and into the throat of the carburetor.
If the float chamber vent were plugged up or non existent the pressure differential would be wrong or not existent and the carburetor would malfunction.
A vacuum, even very slight, placed on the vent hose will reduce the pressure inside the float chamber and thusly reduce the volume of fuel delivered into the venturi of the carburetor.