First things first, turn the needle around. It's the same as the featherweight and like the featherweight, the number one reason for skipping stitches is needle in backwards. Flat to the left, just like the the throat plate.
I'm assuming that the thread is getting caught in the bobbin assembly, not the needle or something. Sucking thread in is most likely to happen if you don't hold the tails. Upper tension set way too low just exacerbates the problem. The other thing that seems to cause it is if there are already threads stuck behind the bobbin case, then they just seem to bring their friends along. Try this:
http://thefeatherweight221factory.co...MachineJam.php
I think it's the Singer Slant Yahoo group that has the service manual... it's dark though and hard to "read" the pictures.