Just bought a 2003 Z400 for my wife. Rear brake wasn't working at all. The owner said he put in a new master cylinder and they needed to be bled. Not sure that's the case but it didn't stop me from buying it as it was the right price.
So from this picture can anyone tell me if you think there is an issue on the small spring? It sure looks like it to me. In the pic I have the brake lever all the way down yet it doesn't pull the "plunger" (highlighted yellow). I don't really know how this should work but it looks odd.

The little spring is just for the brake light.the rod on the back of the lever might need adjusted but try bleeding then first.if no fluid comes out of the bleeder then it's something to do with master cylinder.