If the camera has not been a user or not 'CLA'ed rescently then you need to check the shutter before loading a film. You can do this yourself.
Wind on first, always wind before setting the shutter, depending on model you may gat physical damage or jam, if you dont, (it is meaningful with your Fed2 to adjust speed before you wind as you would be able to tell what you will get, it is not recommended by people who are cautious.)
Remove back and lens and try the slow speed. The shutter curtain should not be badly cracked and should overlap at start and may increase overlap as it is wound, (cocked). If the rubber is cracked the fabric may leak light, through the weave.
When fired at the slow speed (or B) each blind should progress to the other side uniformly, the second blind should hold (at B) until the shutter is released. The shutter should make a repeatable twatwack noise ( at the slow speed) as the 2nd blind is delayed (by the progress of the first) and you should see a whole 36mm opening. The critical think is the sound must repeat, every time, and the blind must close every time.
When you have learned the sound like a grade 8 musician then you can try the 100 it will have a twk sound and the difference characterises the speeds.
If your symptoms seem perfect, then stick in a good quality film as you little camera can take real photos, it is a real camera, and can stretch slow B&W film.
If you have intermittent or capping problems post symptoms. Jay has trained his cats to do camera maintenance - as well as posing, and can more easily help you over the forum noise of clever talking donkeys like me. If you have cracks shine a flash light in dark room through the blind material to see if you can see even a slight leak. It is an addressable problem with black fabric paint but you only need to spot the leak with a fine brush and to leave it to dry flat for 24 hours, before painting the second blind, and letting it dry for 24 hours.
If the problem is only on the slow speed - ignore try a film, a Ru camera will improve your photography but may also improve your maintenance skills
Noel
P.S. If you are worried but still want to try a film take a few shots of a CRT TV raster picture at 2.8 or 3.5 and 1/100! The raster scan and the shutter exposure process interact to allow the acceleration of the first and second blinds to be clearly seen - you dont get a good shot of the screen, just a curved simitar (sabre) shape. The fix (to prejudice Jay's disgnostic) may only be to adjust the two exposed screws on the baseplate, they have strange heads and little locking screws.
P.P.S. Jay likes helping people, and I dont like damaging cameras, posting before risking damage, is clever... ignore humor