Just like in real life, characters in short stories should not talk non-stop unless you want to bore the other characters in your story and bore the reader.
As in real life, what a character has to say in a story will be better received in small doses. The other characters want to talk, too. It’s more interesting that way for the other characters and the reader.
Want examples of how this is done? Go to the sidebar and under Categories click on Flash Fiction Stories. Once you’ve read down to the bottom of one page of stories click on Older Entries for more stories. Notice how the dialogue goes back and forth; because no one likes a blabber mouth–unless the person is a brilliant talker.
Then let them talk.