Looking for some help tracking down a fuel pressure issue. Port & star both idle at 7lbs. At around 3800, port begins to fall off and sometimes dumps right off to 1 above 4500. I get out of it at that point so I’m unsure if I’d lose it completely above 5. Occasionally if I walk it up really slowly, pressure will hold. Things I’ve already tried

-swapped upper&lower pump(both new 2x)
-new fuel lines from tank to carb
-inspected tank, no issues or anti siphon
-swapped senders& gauges from other engine(same result)
-ran fuel line directly into 5gal can to eliminate a tank problem
-lobe seems fine in water pump. Changed oil
-bypassed water separator

i did run it in a hose once while looking in the tank. The only odd thing a noticed was that when throttled back to idle quickly, an air bubble spit out of the pick up tube. I have no idea what would cause air introduction since I’ve replaced every line.

I lightly pressurized the tank. Movement through the vent. Also ran from a gas can on a quick run to eliminate a tank issue.

Check your fuel pressure regulator

The lower is a KE self regulator between 6-8psi. No
other regulators.

560 with -8 lines. The pump should be able to support 800+ hp.

Nobody’s dealt with a similar issue ?

Suction hose collapsing ?