Your problem is one too many carburetors, but I'm sure you really don't want to hear that. Starting fluid is a messy, not very effective way to chase a vacuum leak. A much better method is to use a Propane torch. Turn the gas on, don't light the flame, and pass the torch nozzle around the gaskets and other possible air leak spots. Be sure to pay close attention to the intake-to-head joints. Aftermarket manifolds have a nasty habit of being hard to seal against the cylinder head.

Getting the engine to run as well on two of the same carbs that are designed to support the engine with one of them is going to be a frustrating experience. Dual carb systems are supposed to have much smaller carbs so they can share the fuel metering equally. Two full-sized carbs are definitely the wrong way to go.
Jerry

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