Ouch is right! It sounds to me that he is displaying overstimulation aggression. Once the petting reaches a certain threshold, the cat will reject any further touching and will say "Stop It!" by biting.
Observe your cats body language. Do the pupils dilate? Do the ears flatten or go back? Is his tail flicking? Try reading the body language, so as to avoid getting bitten. If you can only pet him once, leave it at that, and reward him for good behavior. Let him come to you for attention.

The links that K&L posted have some great advice on how to handle different kinds of aggression.

Good luck with this and let us know how it goes!!
**hugs**