Since I havn't seen the camera, I do not know, but I'm presuming it has dry or thick lubricant on the spindle of the drum. This assembly has a drum for the first/opening curtain, two coaxial - top and bottom - rollers for the tapes of the second/closing curtain, and a floating disc that has a pin which works in slots in the top of the drum and top roller to cap the shutter when you wind it. If the disc is sticky on the spindle it can cause this problem, the wider the curtain opening the closer to a full circle the disc travels.Stiff lube on the spindle elsewhere will cause trouble too. This is pretty similar to the design used on say a Leica III or IIIa; here's a link - http://www.pentax-manuals.com/repairs.htm
Originally Posted by Lamar
I have an old Canon IIb that had the same issue, 65 year old lubricant gets almost like shellac.
Edit for clarity
Last edited by E. von Hoegh; 01-07-2014 at 06:25 PM. Click to view previous post history.