custom search not working?

Hi there,

I've added a custom search block to my website but it doesn't seem to function very well. Perhaps I'm doing something wrong.
In the content type the tag field has been added but if I fill in some tags and then search for them in the custom search box they cannot be found. Do I need to add the tags in taxonomy as well? It's not very clear for me.
I've also tried it another way: the words in the text field in my content type can be found but when I add another (long) text field in my content type and try with different words, these are not found?!!

Hope I made myself clear. Perhaps someone can tell me what to do? I'm getting desperate...
Or is there a good alternative for the custom search block?

Thank you in advance!