I take it you mean the diaphragm won'tcome off the slide. OEM diaphragms are not available by themselves, however, you can buy a slide and diaphragm, but they are a little pricy, in Oz at least.
JBM Industries sell a diaphragm, but it isn't the same as the original and also doesn't fit the same as the original. First you have to remove the old one by cutting the plastic ring off. There is a very thin ally overhang on top of the slide, you have to be careful not to damage it as the JBM relies on that to stop the diaphragm from sliding off the top. The JBM diaphragm is a snug fit over the top of the slide but has to be glued to stop the slide from rotating.
I never went down that road as the slide and diaphragm from the UK were $130 each, plus postage, in Oz, and at the time JBM weren't shipping to Oz.
I did play trying to get a diaphragm off a spare set of carbs I had, but found it very difficult. Memory is a little sketchy now, but from memory I used a rotary tool to remove the top plastic ring, that is all I can remember.
JBM are a good source for manifolds and diaphragms BTW, and resident in the US.
i converted to VMs and the two sets of BS38s I had went straight in the bin - where they belong.
Google it, there is all sorts of info available on the web for XS650s.