Why raise on a flush draw? It will disguise your hand. But that's only because nobody would do it. If you are 4 flushing, your odds are low on the turn and by the river, not so good. Why not save your chips for a different hand? You don't even have a pair!

I'm with MitchellC, a nut flush draw - build the pot! Anything less and you might end up with second best flush.