If you suspect that you have a vacuum leak you can use either a unlit propane or acetylene torch. After you start the engine take the unlit torch and move it along the head to manifold areas, carb base and see if the engine smooths out or speeds up. If it does, you have found a vacuum leak. I remember years ago that we had a work truck that was outside and the weather got really cold, carb was a mess and Dads mechanic showed me that using some acetylene down the throat of the carb did the trick to get it started. This might narrow down your source of trouble.
