Reply to "Two fuel pump in serie"

I have essentially the same set up on my car. Many racers do also and will just use the electric pump to prime the carburetor(s) to start the car.
Even the stock mechanical pump is enough to run the car even under race conditions.
Where it helps me is to fill the carbs when the car has been sitting.
Just turning on the ignition key will have the engine primed in 3 or 4 seconds.
In my case, the Pantera-Electronics Engine Controller will then turn off the electric pump and turn it back on as the engine needs it while it is running.
The electric pump is also useful on a hot engine under certain atmospheric conditions (weather) to prevent fuel vapor lock in the fuel line.
The Holley red pump (shown in the picture) is the low pressure pump set at 3 to 4 psi output. That you would use for Weber carbs. The Weber carb(s) is designed to run at that pressure.

The blue pump would be for using with a Holley carb since it is set at 7psi. The Holley is designed to run on that pressure.

The Holley carb needs to be kept wet to keep the fuel bowl gaskets from drying out, shrinking and cracking.

The Weber carbs do not but because of their design, the fuel in the bowls evaporates quickly (about a week or so). They have no gaskets submerged in fuel to dry out or crack.

Leaving the engine sit for a week, the electric pump helps a lot in reducing the stress on the starting motor and mechanical pump to turn the engine over long enough to get fuel into the carburetors.