HELP PLEASE - I want to drive it this summer!
I have been chasing an issue for a couple summers now. Intermittent issue once car is warm, driving or sitting in the driveway.
74 1.8 with L-Jet
If driving, engine starts to bog down, pressing the gas pedal does little to nothing, sometimes get a backfire out the exhaust. Sometimes it will come back to life, sometimes it will die. I hooked up a fuel pressure gauge that I can monitor from the trunk, line isn't long enough to have it in the cockpit while driving. When it behaves this way when sitting, the fuel pressure drops to 0. Today I also noticed that the fuel pump is not running at a constant speed. I have a Bosch 75-76 style fuel pump (replaced a leaky 3 port a few years back). The pump is mounted to the firewall, and it is pretty loud when sitting in the driveway. It sounds like the pump is running at varying speeds, and even stopping for a second or two occasionally.
I thought the pump should be running at a constant speed, with the pressure regulator and return line managing a constant pressure, is this not correct?

Things I have done: All new injectors. New fuel filter. New fuel pump. New fuel sock in tank, and tank cleaned (it is in GREAT condition inside). All new vacuum lines, EXCEPT the big one that goes to the oil fill console. Plugs, wires, cap, rotor. New fuel pressure regulator.

Any ideas?

Had similar issue, the feed line from the tank was kinked, and would not allow enough fuel to pass under acceleration.
I think is was sucking closed.
Replaced the kinked line with stainless braided line and all is good now.

If after inspecting the lines, I might suggest you wire the pump directly via a toggle switch.
If the issue stops when using a toggle switch, you know it’s a sensor/wiring/electrical issue.

I am far from an expert on wiring - can you provide explicit directions on how to wire it up directly? (straight to battery with switch on the positive wire, or tap into a switched hot in the fusebox?)

Thanks

"Straight to battery with switch on the positive wire " will be fine, by doing that you will know if the pumps good or bad as are bypassing the original wiring you can then go back and fault find that if your pump is good.
Good luck.