I had that issue in one that I bought and the hand wheel had thread not only wrapped around it, but somewhat melted. pulled all that out and it sews like a charm.

One other possibility is that there's a short in your armature inside the motor; that's what was happening to mine. It would start off fine, and then 'down-shift' to what was almost a slower, lower gear. That's because the copper plates in the armature were shorting out at that temperature, or when enough dust connected the two plates. A quick replacement, and everything worked great!

WOW, My baby is humming so sweetly now. I surprised DH yesterday. I ran the machine off and on while he was at work.By the time he got home she was purring real nice when I sewed. We never opened up her motor. You guys are good. Thanks for all the encouragement. When I took it to quilting this morning all the gals thought she sounded good and quiet!