Most of the time when your machine bunches underneath like this it is a problem with the top thread, common faults are
- Top thread not threaded correctly (check you have threaded machine as the manual shows)
- Machine threaded with presser foot down (blocks thread passing through tension discs) always ensure presser foot is raised before threading up.
- more serious causes can be if the tension unit has developed a fault.
Rethreading the top thread will usually solve this problem unless there is a more severe problem if that does not work for you then you may need to have your machine inspected by a Pfaff service engineer.