In the end I notice the pump not making a sound at one point, so I hit it and it worked... Turned out to be a faulty pump.
Reminds me of a joke, referring to the old Spica fuel pumps mounted near the gas tank beneath the right rear fender on the early 105 Spiders.
: Why are Alfa lug wrenches shaped like a hockey stick?
.: So you can hit the Spica fuel pump without getting your clothes dirty!