Can you paint over rustoleum primer with auto paint? Will it adhere to it or peel off?

I've done it before for friends on some motorcycle parts that they primed but I still don't think it's a great idea. If it was any kind of project that I cared about I would sand off that primer and use automotive grade stuff. The one bike I did is now 6 years old and he hasn't had any sign of peeling or other problems.