Gasoline will not hurt copper line! But I would be wary of using copper line on a V-Twin due to the vibration at hand. Metallic lines, especially copper and aluminum do not stand up to vibration well. Vibration causes stress-cracking in these metal lines, and you could end up with a fire when gas spills all over your engine! The lines will break at the compression fittings conections!
I had a big compressor at work with copper valve actuator lines, and they kept breaking off due to the vibration. I used some "316SS Swagelok" fittings and SS line to replace the copper lines. It worked like a charm! And stainless line looks pretty cool too.
Still, I'm not sure if I'd trust it for gasline on a bike, unless you used lots of rubber-lined clamp brackets to stop the lines from vibrating and breaking off at the compression fittings. Those brackets are ugly, unless you are building inside a refinery or gas plant.