Help! Has this happened to you?

[Paul462]

My '68 T337C was fitted with normally aspirated IO-360's a while back. The front one has approx. 150 hrs. since factory re-man.

After about 45 mins. flight time, I'll lose fuel pressure on the front engine, and it will start to run rough. I'll apply low boost pump, engine performance will smooth out and return to normal, and I'm good to go for another 30-45 mins, at which time the anomally re-occurs. Continental doesn't think it's the engine-driven fuel pump, but rather a fuel starvation problem or vapor return line blockage (between the engine-driven fuel pump to the fuel tanks).

Both fuel cap vents work, and the wing tip over-board vent is fine. I'm not sure how to test for proper vapor return line functioning.

Any ideas, anyone?