Water leak cylinder head

I have fitted a second hand cylinder head to my 12J engine, new gasket all torqued up etc finished. Put water in and water is running out from the exhaust side. Have I put the gasket on up side down? is it a block and cylinder problem? why is the water coming out. It is a proper run off as though there is a hole but cannot see exactly where it is coming from. I have not run the engine yet. Looking at taking it all apart again or is it something simple and obvious? any ideas please.