it has been my experience that much more than 6" from tank to carb causes problems you are having when fuel is consumed. there is really no need for that much line. unless you have to marshall your own car from the drivers stand, 4" is enough to keep it running for 20- 30 seconds on it's lid.

you have quite a long fuel delivery system. in my opinion you are asking too much of the fuel pump (which is your engine). when tank level gets low the exhaust pressure from the engine cannot keep the 10" pressure line charged enough to push sufficient pressure into the tank's empty space. along with that fact, your engine must draw the fuel through 12" of line basically on it's own if you can't keep the tank pressurized enough.

The probelm lies in the length of your fuel system