I have a new theory. I think using a -6an gravity feed out of the bottom of the surge tank is inadequate. The Bosch is basically sucking the fuel out of that 'straw' since there is very little pressure on the fuel in the surge tank. -6an is plenty for my power level on a pressure line but there is no pressure here...
I shot an email to Full Blown. I think we should lop that -6an fitting off the bottom of the tank and run a -10an to the Bosch instead.
The small line size combined with two 90 degree fittings may just be too much. Here's a photo to show what it looks like:
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