Suspected BCDD problem

[Roberts280Z]

On my '76 non-CA Z, at idle, I have a very noticeable high-pitched Bronx cheer coming from the area of the BCDD.  It's almost a buzzing sound.  After reading everything that I could find, I suspect a rupture in one of the diaphragms.  The sound will vary if you come off idle.  The BCDD seems to still function somewhat properly - that is, holding RPM up for a bit before letting it drop.

I could disassemble it to check the diaphragm(s) condition, but I don't think replacements are available, either for the diaphragms or for the entire BCDD.  I'm aware that some have deleted the BCDD and plugged off the opening.

Having said all that, I should add some background info.  The car hasn't been driven in years, but the engine has been run several times in the last year.  On a couple of occasions, after startup, it has run extremely rich (I have installed an AFR meter) with a very rough idle.  Then, after 10-15 minutes, it will fix itself.  A restart the next day will be fine.  But if it sits for a few weeks, it may fail again.  I mention this as full disclosure, but I sure don't see how a BCDD problem can make it run rich.

So, any suggestions?  Thanks in advance!

Robert