In WordPress, you can select under Options>Reading whether your RSS feed readers will be able to see the complete text of your posts in their readers, or only excerpts. However, even if you select Full Text in those options, if you use the More tag in your posts to manually create excerpts for your blog site, your feed readers will only be able to see that same excerpt.
The Full Text Feed plugin from cavemonkey50.com fixes that problem quickly and easily. Just upload the plugin and activate. If you use Feedburner with your RSS feeds, you may not see the full text feed until you publish a new post.
This plugin is going to be added to my post on Things I do to optimize and secure every WordPress site and blog.