Quote Originally Posted by Abdula
Uh I think I should clear this up. What I mean is that the Kyuubi itself supposedly has limitless chakra I don't mean to suggest that Naruto has access to that amount of chakra as yet. I already said that there is a limit to the amount of chakra he has access to.
At this point I think we determined that its actually the Kyuubi in control at this point. But with only 4 tails, I don't think the Kyuubi has access to all of his own chakra. That what I was saying anyway. So maybe he's using Naruto's because he has this attack, but doesn't have enough chakra to use it with only 4 tails.