A lot of those Ikoflex cameras seem to have bad shutters.
You could always tape up the back w/ electrical tape. I have been doing that on an Argoflex TLR for a year now because I'm too lazy to put seals in it.
Or you can buy some thin foam sheets from Malwart for seal material in their crafts department. I decided that the easiest way is to buy some black knitting yarn from the same place and unravel an appropriate length (you only need one strand, as its too thick w/o unraveling it). Then take a knife and clean out the old stuff in the camera, but don't do a through job. Leave some residue in there, as this will be your "glue" that holds the yarn in. Then cut your yarn to size, stuff it in there w/ a wooded coffee stirrer or the like, and close the camera up and let it sit over night. Easy peasey.