Ariana, did you take the bobbin case apart or the hook base? The bobbin case is the part in the link I gave you to my site. That was only to help you get that screw moving so you could adjust tension.
The hook base, is the part that was here:
http://thefeatherweight221factory.co...MachineJam.php
I am 99.8% sure that this is where your problem lies. It's very possible to have thread caught back there that you can't see without disassembly.
This is what I dug out of one machine from exactly there (yes, I had a hint that it was there, but no idea that there was this much) and yes, the machine had the exact same symptoms you're describing in both posts.
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To add a photo to an existing thread do one of two things:
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If you're using the "Quick Reply" at the bottom of the screen, look at the top of that box, and there's a "picture" icon, just like in the other window when you start the new thread.
If you click on "Go Advanced", it looks pretty much identical to how it did when you started this thread. Same picture icon.
I agree with Miriam, we need to see the bobbin area - without the bobbin case in place preferably, and also if you could post a pic like this one (this is a featherweight, I didn't want to pull the 301 down from above my head)
This is the area I mentioned that would be behind the drip pan right on the other side of where the bobbin case goes.
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From here on, I think we really need photos. We've been operating blind and I think that's why we're going in circles.