With query_posts('p=27'); you request only the post with the ID equal to 27. Does this post exists and have the more tag in the content?
Also note that (taken from WordPress documentation):
If you want to use the Read More functionality with this query, you
will need to set the global $more variable to 0.
And you are setting the global $more variable to 1.
Also be sure to use the more tag in template files intended to display multiple posts: category, archive or index and home (index and home supports more tag only if you have set your home page to show your latest blog entries in the wordpress settings).