About the Kenmore, I have one and I have had it for about 6 years it is a very good one. But much to my dismay the 10$ a spool 100 cotton thread I bought last week jams up in my kenmore.
I thought something was wrong with my machine so I cleaned the bobbin area and everything trying to get it to work and it wouldnt
I put in a cheap 15 cent spool of poly from walmart and it runs like a champ.
I think with all machine they may just have a preference to thread and all you can do is keep trying til you find one that works
By the way quiltluvr if you want Pm me and I will send you my new thread that I cant use to see if it works in your machine.
Its white 100% cotton Aurifil Mako NE 50/2