Electric fuel pump

[Thegearhead]

Hey fellas, A friend of mine told me about this site,with the hope that somebody maybe able to help me out. A customer of mine has a bone stock 40 ford standard. The car sat in a museum for 13 years before he bought it.Needless to say it's had a few issues. The car may sit for a month or two before he may drive it, So he wanted me to install an electric pump to help in the aid of starting it.So I put a 6volt Carter on it,running just off of a toggle switch. I also installed a new mechanical pump and push rod.The problem is that it runs out of fuel on the highway.Around town at 30-35 mph all seems fine.But at 50 it starts to stumble,If I hit the electric for a second and lower the speed it straightens out.Is it possible that the mechanical pump cant pull it fast enough past the electric and it starts to starve? Any help here will be greatly welcomed! I have had the car for two months and it needs to go home! Thanks!