FeedBurner will not process an original feed from your blog if it is greater than 512K in size. (This limitation only applies to the actual size of the feed file itself and does not include any images or media files you may have linked to or embedded in your posts.)

To get a feed larger than 512K back down to size on Blogger, you need to add a parameter to the address for your original feed's URL — the one that FeedBurner checks for updates in order to keep your FeedBurner feed current — that tells Blogger to shorten it to a specific number of posts. To add this parameter:

1. Sign in to your FeedBurner account.
2. Click the title of your FeedBurner feed on the My Feeds page.
3. On the feed management page that appears, click the Edit Feed Details... link just below your feed's title.
4. In the Original Feed Address field, change the address listed there from an example like the following:

1. Code:

   http://myblogname.blogspot.com/atom.xml OR http://myblogname.blogspot.com/feeds/posts/default

   
   
   to the following format:
   
   

   Code:

   http://myblogname.blogspot.com/feeds/posts/default?max-results=3

1. 
   (Note that max-results sets the number of posts you want to have appear in your FeedBurner feed. Any integer value between 1 and 500 is permitted.)
   5.Click Save Feed Details. Your changes are immediately applied and FeedBurner re-burns the newly shortened (or lengthened) feed.

How to tell the filesize of your feed?

Enter its address into www.web-sniffer.net and look at the report it returns; there should be a value in kilobytes for the size of your feed in an "uncompressed" format.