RapidRobert is right, that is a ported vacuum switch. It opens up internally as it gets warm but vacuum is supplied from a hose to the switch. It has no internal vacuum of its own.
You really need to sort out if this is carb or electrical related. Since you have replaced the rest of the electrical system, try taking your Ignition module in to AutoZone and having it tested. Make them test it several times until it gets hot to see if it starts to weaken.
Try spraying some starting fluid in the usual places to check for leaks - around the carb, vacuum hoses, and intake ports. Also, I've had vacuum leaks in the power brake booster do weird things at idle. Try temporarily plugging that hose/port.