Have you fixed your problem yet? If not, I'd be happy to help. Do this:
1. Send me a file you have black trouble with.
2. Tell me what kind of printer/output device you're sending to.
3. Screen shot or write down all the options in your print dialog, so I know how you're sending it to the print device.
4. What version of Illustrator are you using?
Email this info and a "bad black" file to me at:
artboy@artboygrafix.com
~ Brian