What carb are you running? Just wondering if it has it's own filter (like a stock carb), and if it might just be happier with the lower pressure anyway. Some carbs much prefer low pressure vs high.
And ignoring all the other possibilities, for a given volume of flow, won't the larger diameter tubing automatically flow at the same, or a lower pressure by natural laws of physics?
Pushing the same volume of liquid through a smaller opening raises pressure. The reverse is true too, unless the volume of flow is great enough to overcome the loss with the larger hole/tube.
I am probably over-simplifying a more complex issue, but that's what popped into my head right off.
Your two filters prior to the valve are basically one per tank, correct?
And clear filters up top have been the source of much consternation for 50 years when they refuse to fill all the way up while running. Even at half empty, if the engine is running and the float bowl is full, then having air trapped in the filter is not an impediment.
I've seen it both ways, with full filters to half (or less) filled filters while running. Can't explain the dynamics, but it's how they operate sometimes. And with modern (read, crappy) fuel pumps there's probably even more likelihood that both volume and pressure are low enough that they won't overcome the natural tendency for the filter to stay "un-full" even when the pump is pumping.
You can try different things, but if it's running and can handle a long uphill slog on the highway, you should be good.
Maybe that would be a good test. Find a local highway with a long hill if you have such near you, and give that hill a long blast at speed.
Paul
