Gregg –
It’s more likely to be an approach thing than a fly selection thing. Are you coming up on the carp from behind or from in front? Carp are very spooky and sensitive. Have you tried lengthening your leader out to 12′ or so? I like to see how a carp is feeding and then make an early cast into the mud in front of it (I use Crazy Charlies). When it comes over the spot I know my fly is resting on, I puff the mud lightly a few times to draw the carp in.
If you are fishing deeper water, you might try waiting for a warmwater mayfly hatch – carp will sip flies off the surface. Or, you could always go with the last-ditch effort of chumming them in. A box of Wheaties works wonders as chum – just throw a popper into it and wait for the eat.
Zach