Alrighty. I've replaced three mechanical fuel pumps in my 73 240z in the past five months. [Because I initially thought this was the root of all of my problems]
It seems as though the pump loses it's prime every time she sits for a week or two.
For example, today: oem-spec fuel filter is clean and new. The filter is full of gas. Car will not start with a solid 2 minutes of cranking. No fuel is making it to carbs. What gives? It's like the pump is sitting there doing nothing.
I can blow gas through and suck gas in from the supply line easily. Gas tank is fairly clean--fuel filters have never been dirty in the past 6 years of ownership.
SU floats have been set 3 times, mixture nuts 2.5 turns down. Losing my mind here!
My two next steps:
Remove valve cover to inspect eccentric gear and activate pump by hand.
Remove OEM fuel rail and check for debris (is this even a likely culprit?).
I am already planning an electric fuel pump install because I'm so tired of this.
Here are the threads I looked into: