[m1franck]

The '71 fuel pump did have 3 lines to/from it. 1 in from the fuel tank, 1 out to the carbs and 1 return to the fuel tank. Sounds like your factory pump had been replaced with something else. Got a photo of it?

Fuel pumps push fuel better than they pull fuel. Also, fuel pumps last longer when they are not installed right next to the exhaust system, like on your '71. On my '71 911T I removed my stock Bosch fuel pump located near the left rear wheel well in order to make room for upgraded rear sway bar mounts and to use a fuel pump that was readily available and priced reasonably.

I installed an Airtex #E8337, 9PSI - 30GPH fuel pump up at the fuel tank and retained the fully recirculating fuel system by installing a PMO fuel pressure regulator in the engine compartment. Also, tapped into the stock fuel pump power wire, which passes conveniently near the pedal cluster, then rerouted it to the new fuel pump. Photos below show the work in progress of that conversion.