Are you using a heavy bobbin thread? I still have the one that came with my machine. It is possible to get a download that doesn't work well. I download lots of free things and some work better than others.
What are you trying to put it on? I did some name logo's on knit shirts and it was difficult to get it to work nicely no mater what stabilizer I used.
good luck in sewing!
Sally aka Nana24

You will need to use "bobbin Thread" in the bobbin. It's much thinner than regular thread. Also you may need to adjust your tension.

I changed the needle and haven't had that problem anymore, whew!!
Thanks for everyone's help.

Most likely, if your built in lettering works on the same material, then yes, you have a bad design. Beware of free designs on the web, just like free anything else. A bad design will never work correctly. Sometimes they have been re-sized from larger designs and now the stitch density is way to high and you just can't run it.

I keep having problems with thread bunching. I have brought the machine in for this several times for this same thing. The last time the manager had the repair person change the bobin case. I haven't tried it very much since. I am afraid to mess up something again. Hope this works.