Colours in Illustrator

Not quite sure about this one, but if you look at separations in you pdf file you can see if anything is wrong. Be sure to have overprint preview turned on in Acrobat

Did you remove all unused swatches, symbols, brushes, graphic styles check for stray points etc.?

If you want to make certain that CMYK does not show up then substitute the cmyk black with a pantone black.

What's the art????

Some items cause spot to be converted to processes -- Meshes, blends, gradients.....

In most spot files CMYK are always included because RIPS expect to see those plates. Just because the plates are listed it doesn't mean there is art on them. As Steve posted, check the seps in Acrobat Pro. Is there actually art on those plates?

Good Idea!!

I use to have this problem, must try this idea next time.