At a place I used to work in Richardson, Texas, we had a guy "fix" his fuel line with a section of copper from the fuel pump to the carb. About two weeks later, I saw his big Ford Galaxy on the 10 o'clock news.....on fire. He said that he was driving along and the thing caught fire. The nearest house was 1/2 mile away (before cell phones) and he had to walk (run). The fire dept saved the tail lights and rear bumper.

Copper for fuel lines or brake lines is not a good idea, especially since steel lines are soooooo cheap.