If these engines are stored to a long time with fuel in them, that's the problem. The light part of the gas will eventually evaporate, leaving the gelatin of the fuel as a residue. As it slowly dries out, it will get hard a crusty. New gas won't dissolve old gas, so you are left cleaning the insides of the carbs. Should run much better after a good cleaning with a carb cleaner. That's the only thing that will touch the dried fuel residue. Other areas that are not vented (like the carbs are) may not be much of a problem, such as the fuel pump or hoses. They are not open directly to the air. You may have to replace all the rubber fuel components, for another reason, though. If the engine dates back to the late 79's or very early 80's and has original fuel components-the rubber parts of the fuel system were not made to handle today's ethanol fuels. That includes all fuel hoses and the rubber bladders in the fuel pumps. Usually when these old hoses start to go, they disintegrate and black bits of hose will migrate through the system and fill the fuel bowls. I don't see that in your pictures, but then I cant' get much an enlargement on them, either.
