Try disconnecting and plugging the vacuum advance line at the distributor and revving the engine with the advance disabled. If the problem goes away, find the open or short circuit between the distributor housing and the condenser, and/or replace the wire between the coil (-) terminal and the side of the distributor. You might be chasing an electrical gremlin by working on the carburetor- - - -which can be VERY frustrating!
Jerry
BTW... I did disconnect and plug the vacuum advance line at the distributor and revved it up but had the same issue!
