Singer SS diagnostic question for you.
OK, I am working on a 1946 vintage Singer straight stitch, gear driven, rotary hook, vertical end loading machine.
{( I'm not going to mention the model # at this time, as I don't want to prejudice the issue. )}
At slow speeds the machine sews beautifully. Perfect top and bottom tension with any thread put on it.
However ~ = ~
At high speeds the top thread looses it perfect tension, and wants to occasionally loop and skip stitches under the fabric.
I know the needle is correct and is in properly, threaded properly, that the bobbin is wound and threaded properly and the tensions are correct. Otherwise it would not sew as good as it does at low speeds.
Nothing I have done to date has corrected this. I can improve it by cranking in more top tension, but that is not a cure. Something is not right.
Now the question: What is your theory as to why this machine is doing this?
Joe