Have you used those tips on your Aztec at all before? What type of paint do you spray? You may have also overtightened the tips, or are completely closing off the needle.
With my Aztec, I spray only acrylics, and after each session, I remove the tip, separate the needle tip, and dump them both into windex window washing fluid, and let them soak there for a good 24 hours. At that point, I'll rinse out with water, and they're as good as new. I'll also soak the gravity cup and lid. I've had a lot of problems trying to use the siphon caps, and have just stopped using them alltogether, since there are usually problems with them.