Larger fuel lines are often required for racing, especially on vehicles where the engines can be modified for much higher RPM.
Larger fuel lines on a street driven or even more so, a parade vehicle contribute to "heat soak" issues, and hard starting hot issues. The larger diameter slows the fuel velocity causing the fuel to run hotter, or even vaporize in the lines. The additional capacity allows for more fuel to be dumped into the carburetor on a hot engine at shutdown.
The stock line size is sufficient for a stock vehicle. Billions of miles were driven using stock sizes. My opinion, one of the worse fuel system modifications which can be made for a stock or mostly stock vehicle.
Jon
