I had the same issue with the older shorties. Try this:
1. Look at the "ash cap" and you will see two little vents, right where it meets the battery tube. Cover one of those with your finger to see if that helps. If you like that, skip down to #3.
2. Take a round wooden toothpick and stick the tip in one of the little air holes just under the
threads on the battery connector. Break it off and then use a fingernail or something to make sure its in there good & tight. Put a carto on it and try again, with and without doing #1.
3. Fill in one of those "ash cap" vents. You can use gel super glue or whatever you like. Or you can remove the "ash cap" to fill it in however you wish. Just grab it gently with a pair of pliers, twist & pull to get it out. It will push in with your fingers and stay nicely.
Hope this helps.