Had another lesson in KISS yesterday.
Pulled out the 301 to finally give her a quilt to sew on, and for the life of me couldn't figure out why the top thread was making little loops on the back of the fabric. She worked just fine when I put her away last time! Looked at the bobbin...nothing. Cranked up the top tension...nothing. Then I thought what are they always saying on the QB? Bottom problems are top tension problems. Walked away. Sat back down, gave the old girl a pat and promised not to do anything drastic to her. Followed my threading from the needle up. Urm...ooops! I had pulled the thread in front of the tension discs instead of between them. Easy to do and not so easy to spot at a glance. Rethreaded her properly and all was well again.
So, thanks for keeping me from lots of frustration y'all!