Here's a tip I shared on Facebook and on Sew Simple of Lynchburg's blog (my bricks and mortar shop and Janome dealership):
If you are using a horizontal spool pin on your machine (sideways), you need to use a spool cap.
A spool cap (sometimes called a spool holder) holds the spool or cone on the pin. These usually come in two sizes (there’s a third type I’ll talk about in a minute) and are meant to not only keep the spool from coming off the pin, but to hold the thread slightly away from the actual spool. This keeps the thread from getting snagged on the spool, especially if it’s an older spool with the notched edges and a slot cut in it for the thread end.
Enter thread that is cross wound on a mini-cone or spool like the large spools of Aurifil.....
These threads are wound in such a way that they are meant to be fed off the top of the spool/cone without any interference from a spool cap. If you use a separate cone stand, that's great. But many use the horizontal spool pin on their machine. Some may use a spool pin, others don't, but the cone doesn't look entirely right on it.
While the cone is full, it's rarely an issue. As the thread is used up though, it can get hung up on the small spool cap. Without a cap, a nearly empty cone can start to 'dance' on the pin as it unwinds.
I've got a solution for you:
This is a Janome product which fits on the horizontal spool pins of all Janomes (Kenmore and Elna machines as well, I expect). The larger, new machines come with them, so check your accessories for it. Some of my students tell me that other brands are also making these special spool caps now.
I do sell them online at Amy's Quilting Adventures, but I also suggest you check with your local dealer.
If you liked this tip, you might want to read the whole article I wrote for Sew Simple. It's part of a series on troubleshooting mysterious machine issues.