You need to remove all rubber parts such as diaphams, choke plunger seats,butterfly shaft seals etc. If all the rubber parts are removed, then should be OK to soak them.
Soaking old carbs may be fine for a general clean up, but the important thing is to make sure that all passage ways and orifices are clear. Those unfamiliar with these carbs, seem to fail to check the pilot circuit and the choke circuit. In the "Tech" section you should read up on "carbs".