I had bought a used Janome and had trouble with the same problem as you with the machine running so fast every time I pushed the foot pedal. I took it back to the dealer and they replaced the whole cord and foot pedal at no cost. I felt very lucky and now it works great. Good luck to you to find out your problem.

Thanks for advice. Manual doesn't mention speed. It's a $100 beginner Brother which works very well but speed is not adjustable. Thanks for the advice on putting a wedge or using left foot. I'll have to inspect it to see if possible for wedge. Appreciate all responses.

Did you look on the machine itself? Sometimes there is a lever/dial right on the front-facing you.

I do,not wear a shoe on the foot that controls my foot pedal because I can feel,how hard I am pressing when I do,not have a shoe on.