I think you just need to add the cables that are obviously missing... clutch cable, brake cable, throttle cable. You know, the ones that run along the handlebars and are very visible. Those alone will go a long way toward making the model look more realistic. You can wire the engine (spark plug wires) and run oil lines, too, but those aren't as visible or obvious. As far as where to get the material... usually the best thing to use for motorcycle cables is hollow vinyl tubing, because it bends and forms realistic, smooth curves. The bikes I build are 1/9 scale, and that tubing is included in the kit.
Not sure where you would find it otherwise, though... maybe if you found some insulated wire and pulled out the wire inside, leaving just the vinyl insulation? Old telephone wire, maybe?