Ok so searched high and low for this and finally found out that it was my theme that I had added which was wrong. Look for feed_rss2.php in wp-includes and look for some code in there, that uses use_excerpt_rss my theme used this whether the rss setting->full (rather than summary) was selected or not in the settings->reading.
If you change the else to be “the_content()” rather than “the_excerpt_rss()” it works. Your images are sent in the description so then the rss readers can read the whole article.