For some time, I have been aware that my RSS feed was broken. That result is bad.
This post describes what I did to fix the feed in seven steps.
I put my feed into the W3C Feed Validator: http://validator.w3.org/feed/
The feed validator indicated that I had many “high characters” in my UTF-8 encoded website.
I validated that UTF-8 was the setting under Settings — Reading — Encoding for pages and feeds. For blogs originally published in English, the UTF-8 encoding is currently the best recommendation. Other encodings are possible, but the generally recommended consensus is to stay with UTF-8.
I validated that my PHP database is also encoded as UTF-8. Some people have databases with other encoding schemes, completely explaining the issue. Others mention coding in the wp-config.php file, but I noticed that the wp-db.php file has its own logic for correcting unspecified encoding (setting the value to UTF-8). Whether that situation is true depends on your version of WordPress.
The W3C validator still indicated that some posts had these high characters. What I believe happened over time is that I cut-and-pasted from another program (perhaps Windows Notepad or Microsoft Word) into the WordPress text editor. I do not cut-and-paste all the time. However, I believe those times are when the high-encoded characters entered into the post. The response is to fix those posts by simply editing them in the WordPress text editor. In my case, the characters were associated with what appeared to be a space. I deleted characters around the offending character and then updated the post.
After each removal, I refreshed the W3C Validator, and saw improvement in the RSS feed errors. In my case, many of my posts have thetag inserted. I did not have to edit text beyond that inserted tag to make the RSS feed work. If I were more complete, I would instead go through the whole post and make changes to the whole text.
Once the validator provided a clean feed, I could then see the correct feed. For this blog, the RSS feed appears at http://www.marktab.net/datamining/feed/
Try the Validator: