They're made to get hot - when you're stopping and starting, the breaks in between sewing allow the foot control to cool down. When you're sewing steadily at less than full speed, the extra electricity is dissipated as heat. They can get VERY hot - if you have nylon carpet, they can get hot enough to flatten the carpet.
When I get a "new" vintage machine, I replace all those bakelite foot controls with modern electronic controls and new cords. They're smoother to operate, they don't get hot and they don't cause fatigue trying to maintain a steady speed. It's easier to find the speed that you want and keep it there. They're well worth the small investment, to me.
