He does not have the Kyuubi's chakra. He sealed it inside himself and then sealed himself into a shinigami. When he met Naruto, that was using some of his own chakra that was sealed in Naruto before Minato died.
If you want to ignore the technical reason, here's another reason: Besides, that would defeat the purpose of only giving Naruto half the Kyuubi's power. The full extent of Kurama's power would be too much for him ot handle all at once. It was hard enough for Naruto to control half the Kyuubi, and when Minato met with Naruto, Naruto was nearly dead because of the Kyuubi taking over. Giving Naruto more of Kurama's chakra would also give Kurama more willpower. They weren't friends at that point.
