Sandpaper or a sharp knife. Most motors are wound with Class 200 magnet wire. if you try to burn it off it will have to get too hot and could damage the windings. We use the sandpaper method in the production of transformers and coils for power supplies. There are also abrasive strippers available that use fiber cones but they are not readily available to most people. I have found that 320 grit emery cloth works well for the size wire used in our motors.
Thanks for the help. What colour should the wire become? I could only get it to a light brown colour, where it stutters on startup and spins with much less power than the other motors, indicating that the wire in question is partially connected