Only have 3.5 mechanics working in the back, so I won't call it a big shop. Last Monday I had six carbs by myself. I have seen everything in the carb, dirt, gum, varnish, jelly, corrosion, etc. Have seen needles frozen in the bushing and I have one needle, which I saved, where the plating on the needle is peeling off. Viton tips and seats swelling up are the major problem. We buy Tecumseh part number 631021B and Briggs part number 398188 fifty at a time. Never had this type of problems until about 5 years ago. Before that may have seen one carb problem like this a week. Today's carbs are designed to run so lean and the jets and passageways so small, that it doesn't take much to create a problem.