Just installed a new tank and pump.... now not working!

[chevymotocross]

I really want to cry. For those of you who have replaced a fuel tank on a 73-87, you know how difficult it is. I got a new tank, and carter pump and strainer for my 87. It took me litterally 4 hours to line everything up and I finally got it. I put a little bit of fuel in, to make sure she would start and run on that tank. She fired up and ran for about 30 seconds. I turned it off, and drove to the gas station on my other fuel tank. I put $10 of fuel in, select the switch over to that tank. My gauge goes way past full and it won't start or run on that tank I think I would like to scream.