Fuel presssure drop

[68Formula]

I once had the problem because the line was too close to the valve cover. Fixed it using a swivel connecting at the carb inlet and bending the metal portion up so the flexible hose was even with the carb inlet.

You can test it using an insulating sleeve or temporarily routing it away from the exhaust and heads (zip ties?).

If the problem is repeatable at idle, you could get the engine warm, and then hook the pump inlet to an external tank (TANK OUTSIDE AND AWAY FROM ANYTHING YOU DON'T WANT TO CATCH ON FIRE). At least then you know if the tank is contributing.