When I had the intake manifold off for polishing, I noticed there was a layer of black stuff (oil vapor/carbon from the rocker box) inside, so I tried to clean that out too. I tried Gunk Foamy, and several cans of carbureter spray. From the brown liquid that came out, I concluded that some of the black stuff came off, but when you looked in the throttle hole, you could still see it was there. I even tried a treatment of Seafoam, which is typically for carbon deposites on the valves and cylinder head, but this stuff was stubborn. Is there any other way to get the carbon out of the intake manifold, besides taking it off and using some kind of industrial treatrment? the engine is together and nicely detailed, so I don't want to mess with the outsides.