Problems with More tag

I'm editing my first post, and am trying to specify the cut-off point of the post using the 'More' tag. However, try as I might, I cannot get the tag to function correctly.

I've checked that the More tag is not nested within any other HTML tags in the editor. I've also looked at the theme's function.php and post-template.php files to see if the theme is using the_excerpt(). Although I found code referencing use of the_excerpt() in the post-template.php file, there does not appear to be a predetermined limit of 55 words in function.php. I should mention that I haven't made any changes to this document yet, as my understanding of how this code works isn't exactly advanced.

Everything else with the code for the post seems to work correctly, but adding the More tag always shows the next two words that follow it, instead of cutting off cleanly where I want it to.

This is driving me crazy, as the post preview looks awful with these two rogue extra words after the More tag.

As this is the blog's first post, I published a second (test) post to see whether this would make a difference. Not only does the problem persist (same two extra words, 'Describe Boston', showing up before "Read more"), but use of the More tag in the second test post is also working incorrectly. There are four extra words displayed before "Read more" in the second post, which leads me to believe it MUST be a problem with the_excerpt() in the post-template.php.

Thanks in advance for any help or suggestions.