You can prove if it is the foot pedal by using it on another machine or trying another foot pedal on yours. Make sure
your belt isn't tight. Featherweights like loose belts. Weak motors are a common problem with featherweights.
You can service your motor with new brushes and polishing the commutator. If any oil has gotten into the brush
area there will be a burned on film on the commutator brush area and it will make the motor run weak.