I added these to my other thread but thought a new thread might get more attention.
Boat is a 1996 Sunsation Dominator
Twin 502s, mildly modified by prior owner(s)
Originally VST equipped, were updated to Cool Fuel II
Keihin Injectors / MEFI 1

Key On / Engine Off, Fuel pressures show 40 PSI, then drop to 34-36 after pump stops running.

Videos below show behavior while on plane, accelerating through powerband until they hit a wall at 4400-4500rpm.

Would appreciate any input about the behavior of the fuel pressures in these clips. Thanks!

If the gauge is accurate, it's just a little low.
Cool fuel has a 43psi Reg and the VST came with a 37psi Reg.

The VST Reg is on the fuel rail and return line goes back to the VST.

The cool fuel Reg is on the module and returns to the fuel filter.

Was the fuel return from rail to VST plugged or something different?

Gauges are pretty accurate. Manufacturer bench tested them and I verified upon receipt.

It appears that whoever modified the system, installed the blockoff plug in the regulator on the fuel rail like the cool fuel systems had.
The rear of the fuel rail is open where the return line would have been.

I replaced the regulator on the Stbd motor with the 43 psi part number (861126A1). When I jumper 12V+ to the gray wire at the fuel pump relay, and let the pump run, I get 40 PSI (not 43 psi) on both motors (leading me to believe that the port motor has the same 43 psi regulator on it).

Where is the regulator located now? Before or after the fuel rails?

43psi Reg and fuel pump is not keeping up, possibility due to injectors are to large, fuel table is pig rich

If compression is good, then my guess is plugs are black

From the vids neither hits 40 psi full load.
when you remove vac line to reg for a second, what psi do you get ?

Regulator is in cool fuel assembly under port side of motor (at fuel cooler). So, before the rails.

I don't remember exactly -- but it isn't 40 psi. Probably 34-36 ish.

Tune is unknown. I'll pull some plugs this week and report back.

Rain cleared up so I grabbed plugs 1,2,3 out of the Stbd motor. Certainly don't look black to me...