I have a friend who had an issue with a Rochester B. It had an annoying stumble upon acceleration in first gear and the plugs were always sooty. I suspected the dreaded warped casting.
I climbed into the engine bay while it was running so I could look straight down into the carburetor while opening the the throttle. At idle, I could see wetness (fuel) appear at the parting line of the top casting and the body of the carburetor where the gasket is. As the throttle was held slightly open, the fuel evaporated, but would reappear once the throttle was closed.
I am guessing that wetness (fuel) was coming from somewhere which it was not supposed to, and was then passing through the gap where the gasket could not seal, creating a rich condition at idle, causing sooty plugs, and incorrect fuel/air delivery upon acceleration, causing his stumble.
