When I am sewing, the machine does fine and then it like quits feeding the fabric through and knots up on the bottom. Does anyone know what might be the cause? it's a viking machine. Any suggestions would be greatly appreciated.

sounds like a threading problem. Take out your bobbin and re thread it, then take out the top thread completely and rethread it. That should fix it. I have a viking and mine does that sometimes if I didn't thread it correctly

I agree with feffertim. Also check that the needle is inserted correctly.

When was the last time you cleaned out the feed dogs?

is the top thread jumping out of the take up lever?

There might be a wad of lint under or near the bobbin case. I would take it out and clean it.

Agree. Sometimes if it's a different weight thread in the bobbin it might do that too with a Viking.

Yep. I have 3 vikings and they all do this occasionally. I always check this first. I'm to the point where I can hear the difference in stitching and can catch it quicker.