Spawning fish have more important things on their mind than eating. Your better off looking for feeding fish rooting around on the bottom and casting to them. My best luck with carp has been putting a weighted fly on the bottom right in front of them or swimming it up to them and dropping it in front of them. If they don't see it at first, hop it a little bit to get their attention. My carp fishing so far has been limited to rivers so far though, so people with more experience will give you more advice.

There's also a book I got for Christmas, Carp on the Fly, that is a great resource if your just getting started carp fishing and are serious about learning more about it. I haven't read through the whole thing yet, but its where I turn when I can't figure them out.