Holley/Demon Carb stumble

EFI to Carb Dual Stage Fuel Pressure Regulator – Aeromotive, Inc

I guess for me to fuel system as a whole is still a bit of a question mark.
For the easy test, I’d get a cheap gauge and plumb it up with some rubber line and tape it to the windshield and see what it reads when the motor is laying down in high gear.
“In theory”, if the system is 100% capable....... the gauge should read the same at that point as it does at idle.
If it won’t hold 9psi(the current setting), then I’d drop the setting to whatever the gauge read at the top of high gear, and see if the pump will maintain whatever that pressure is.

If there is currently a single regulator in the system, and as it sits the pressure doesn’t hold steady at wot for the entire pass....... I’d probably piggy back a couple of regulators.........since the dual stage thing is pretty pricey.
I’d have the first stage go from the 87psi pump pressure down to about 20-25psi, then the second stage from that 20-25 down to 6-ish.

My friends Stocker runs a magna-fuel 500 pump, #10 line from the pump to the reg, #8 to the carb......... gauge never moves from wherever you set it.
I think his pump would maintain 6.5psi if it was 1/2 worn out.