At the risk of being obvious, make sure the restrictor went into the "return" leg and not the "feed" leg. As you say, depending on the fuel inlet flow the return might allow too much fuel to bypass the carb under high demands.
Make sure to get a quiet pump. My (high capacity 240l/h) Bosch 044 is terribly noisy.
www.holley.com
Which model Pierburg did you install?
Glad you got it fixed, but did you ever check the tank venting as Carl suggested earlier? If the tank venting is inadequate, a better pump could just mask the problem (and eventually damage the tank).
I couldn't agree with you more, Bernice. On both my X and 124, I have had Facet pump failures I thought were way too early (and extremely inconvenient). I have resorted to keeping spare pumps in both vehicles.
Not saying it wont work, but probably not the best option. It would give the fuel regulator a marathon workout. Forcing it to open to the return line to frequently and too long with little time shut. (assuming a higher flow rate). That could cause some inconsistent spikes in fuel pressure. FI pumps are designed to work more in the 40psi range. There is a big difference between 1.5 psi - 3psi and 40 psi, and the regulators are designed to work best at a specific pressure range. 40psi into a 1.5psi regulator could be outside its workable range or damage the regulator. Its also possible that the seals on the lower pressure regulator may not be designed to handle the higher pressure, and could cause premature leaking. Obviously, the system wouldn't be operating at 40psi, if the regulator was adjusting the system to 1.5psi, and there was an adequate sized non-restrictive return line, but my point is, the low pressure regulator could potentially see higher pressures with a higher flow higher pressure FI pump than it would normally see with an appropriate matched low pressure Carb Fuel Pump. Obviously, whether it would work would depend on the specs of the Fuel Pressure regulator and fuel pump. If the FI Fuel pump had a flow rate near equivalent to that of the original carb fuel pump, or flow matched to the carb's draw, it would likely work out ok, as it would also be better matched to the fuel regulator. I also question whether FI pumps by design actually last longer. I've had plenty of FI pumps fail on my Vettes. Id suggest two alternative solutions. 1) Find a reliable brand fuel pump of proper type. or 2) go with a parallel Dual Pump system. So what if one pump fails, if you got a 2nd one pumping simultaneously. Would still need to verify that the fuel line feeds and returns were of adequate size for the flow of the dual pumps, without to much pressure increase or flow loss, but most stock fuel line sizes can handle the addl flow. And would work best with a "return style pressure regulator". Sure two pumps increases pressure and flow too. But My point is, if gonna put in a non-standard system, because reliability is the goal, why not go all the way.