The belt needs to be as loose as it can be without slipping. Since the problem came on suddenly, I'd check the foot controller, look for a stray thread, or when was the last time the motor was serviced?

Cari

I'm increasingly sure the foot pedal is the problem. Yesterday it got hot and that's when it just quit. Had noticed it being warm for a couple of days. The motor did not get hot and the hand wheel still turns freely so I guess a new pedal is in my future. In the mean time my 404 has been neglected of late. So she gets to play for awhile.

Update - new foot pedal ordered and received. She's purring like a kitten and sewing beautifully now.
Thanks to all for the info and I will put in a good word for the prompt delivery of my new pedal from sewing pans dot com.

That was sewing parts dot com. Crazy auto correct !