Oh, your running one of them thermostatic vaccum switches. That switch basically, opens up or provides vacuum based on the temp of the coolant in the manifold. I am really not familiar with that in depth and wouldnt know if that would cause problems if that switch was going bad. I would start looking at the items Crazecars suggested. You also mentioned you have a rebuilt carb, wondering if you might be having problems with the idle circuit or with something being stuck here and there.
