I too got a hold of a used carb and this is what I did to clean it up: I purchased a can of carb and parts cleaner (the one with the dip basket only cost $10), took the carb apart, removed all rubber and plastic parts, and let the metal parts soak in the solvent for about a half hour. That loosened up the varnish and dried up fuel real good. Then following the instructions on the carb cleaner can I rinsed the parts in water, dried them up the best i could and liberally applied WD-40 to get more of the water out. The carb looks really nice now. I believe all dirt bikers should have a parts washer, even just the simple cheap one like I used, because you can find a lot more uses for it that just a one time carb overhaul.