probably asking too much from the pump. they will only create so much vacuum to pull fuel. 1/2" line will diminish that signal plus the check valve (how much vacuum does it take to open the valve least wise pull something thru it?), and the mech pump won't pull thru a vane pump. the 6903 only has a 1/4" i.d. feed orifice in the bowl. the pump can be reworked and helped; I have done it. the high pressure does pull some fuel but you'd have to figure a way to regulate the pressure. I've had some of those carter electrics get stuck and sometimes they're a little short on pressure.