Its all about inside diameter. Brake lines have a thicker wall to withstand all that pressure. Fuel lines have a much thinner wall and greater cross section as they only see 5-10PSI on carbureted engines.
As long as the line lets the proper volume through (IIRC like a pint a minute.. its in the manuals). Since restrictions create pressure, you *might* have an issue with the pump not making enough pressure to push enough fuel to the carb. That's about all I can think of.
