Intermittent fuel starvation on 454

Once again....I am back to a fuel starvation issue??? To recap....twin 1986 454's We identified the possible problem last time to running Micron 2's instead of 10's. That seemed to fix the problem. (10 hrs running no issues) However, my most recent outing. The same freakin situation. With full fuel tanks....run for 2 hrs at 2500 rpms. (no problems) on the return leg at about 1 hr into the run....the Port engine stalls. I restart and nurse the rpms to 1500 back to home harbor. I have installed a vacum guage on top of the Racor 500's and it definately went into the red. (5-7 is normal and it popped up to 13) It would stay just out of the red (10) at 1500 rpms. I don't believe I have a fuel vent issue...it seems good. I had the fuel tank polished as I thought maybe a loose piece was clogging the fuel pick-up tube. Could the anti-siphon valve be sticking...would that cause intermitten issues??? Should I replace the fuel lines....they are old...but don't look cracked or horrible on the outside. I did not switch on the cross-over valve this time. (did not think of it at the time) Finally I did pull the filter with 10 hrs on it and it looked fine. I am stumped. Any thoughts....you guys have always batted a 1000 of the rest of my issues.....but this is starting to feel like a swing and a miss.

I forgot if we covered this last time, but why not run with 30 micron filters for your carb motors? The vacuum gauge is an excellent aid. It appears to be showing your new 10 micron filters are again clogged. Do you have fiberglass tanks?

If the vaccum went into the red there is a restriction somewhere between the filter and the fuel. Anything in between should be investigated. Anti-syphon valves have a knack for going bad. Many boats don't need them; they can be removed for evaluation (temporarily). the other possibilities would be stuff in the tank clogging the screen on the pickup tube, the old fuel line collapsing, or the vent line filling with water (from the hull spray).

Just because the tank was polished doesn't mean there can't be something in there (if you have taken on fuel since the polish).

If the wind was off the port bow on the ride back, I'd start with the vent line. I prefer a straight drop (no low spots that would form traps).

I still don't believe its something in the fuel tank as I only added 25 gallons since the polishing...and the Stbd tank is issue free. The wind was coming from the Stbd side and since the hull is a Ed Monk design and where the fuel vent is....I have no issue with water clogging the vent as spray tends to stay off the boat pretty good. (the racors are also showing no water in the bowl for 14+ hours of running so theres that too.) So I think it's narrowed down to fuel line or anti-siphon valve. I will replace the fuel lines but am strongly considering removing the anti siphon valve. What determines if that is a bad move or not?? A $5 part not needed will eliminate another possible culprit. As always thanks for the advice...its very much appreciated from all contributors.

The ASV is highly suspect. You can usually inspect them successfully after removal. YOu may find some debris in the ball/seat area.
MM: on the vent hose. You want a high loop over the vent, then as straight a run as possible to the tank, without a low spot, correct?

The need for the anti-syphon valve is driven by the geometry of the fuel system parts in your hull. In essence, If your tanks are lower than the fuel pump, they are not needed. Personally, I suscribe to your philosophy of less parts is better.

DD - on the vent hose, I think ABYC actually suggests a loop (trap). I have had nothing but problems on boats with dips/loops/traps. I have always had to run them 'straight down' due to the existing hole for the vent line. I see nothing wrong with a loop above the vent fitting. If the vent fitting is properly shielded, I don't see a need for it either.