I'll state this as someone who isn't attracted at all to femboy stuff in general : If the "femboy" is indeed resembling a woman, our brain gets tricked by the signals and just thinks it's a woman, so 0% gay.
Thing is, the "primal" part of our brain is clearly not as effective as we think it is. When feminists are crying that men "objectify" them, they are kind of right. For our instincts, "women" is like an object, with several body parts and behaviors stocked inside. And each one of them has the capacity of arousing us depending on our sexuality.