Radiator problem

[Steve]

So I recently bought a street 04 Gixxer 600 and converted it to a track bike. I did have to replace the radiator due to the fact there was hole in the one that was on the bike. I bought a used one off eBay, took off the fan and installed it. The problem is, all the water is backing up in to the overflow and essentially spilling over in to the bellypan. And I'm not just talking a 1/2 a cup or something. I basically had to fill the entire radiator.

So my question is, is the radiator faulty or do I need to connect or wire something since I removed the fan? It seemed pretty straight-forward when I did it but I may be missing something.