The way I learned it was like this: The stocker puts out about 5 psi...your turbo is gonna put out ~9psi (high estimate) to the venturi so its going to want to push pressure back into the fuel bowl through the boosters, but that pressure is going be inside the (non vented to atmosphere) bowl too so its going to want to push the fuel out at the same pressure, so your back to a delta of 0, no imbalance within the carb. Now the poor fuel pump is still only pushing 5 psi and thats never gonna get fuel into a 9psi bowl so you need to increase the spring pressure in the fuel pump itself. And the way you do that is to pressurize the back side of the pulsator diaphragm with compressed air at the weep hole, creating a pneumatic spring on top of the mechanical spring. Mechanical fuel pumps push the pulsator diaphragm with a spring, not a rod. That way the pump can maintain a certain PSI over its operating range. When the fuel pressure demand is very light the spring barely moves the diaphragm as its still somewhat pressurized on the carb side, when its demand is greater (WOT) its allowed to push with a longer stroke as the pressure to the carb is not pushing back on the diaphragm as much. Much easier to see than to explain. The boosted pressure behind the normally vented backside of the diaphragm provides that much more force to the diaphragm to pump fuel into the pressurized bowl and that is magically 1:1. for every "pound" of boost there is an equal amount of pressure added to the fuel pressure. now your 5psi pump is pumping at 14psi until the boost settles down and the pump follows suit. Check Allpar
Turbocharged slant six: cheap power and gas mileage... or any boost referenced fuel pump:
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Carbureted applications will require higher fuel pressures. The simplest method is to drill into your fuel pump's vent hole, epoxy a tube into the hole, and run your boost to that port. The vent is a reference and if you increase the pressure above the diaphragm, then the fuel pressure will increase by the same amount. Do not connect this port to the bottom of the carburetor. You don't want vacuum, just boost. Someplace between the turbo and carburetor is best..."