Hi!
Try to turn off the Fulltext search option, it might help your case, you can read about it in the faq: http://wp-dreams.com/faqs/the-search-is-not-properly-searching-some-3-or-less-letter-characters/
Also, if you are using polaroid styled results, then posts without images are ignored by default. You can change that as well: http://i.imgur.com/gJx0juI.png