No problem, as mentioned, bad fuel or dirty fuel systems are hell on carbs. I recomend a mild cleaner like Simple Green to clean them, harsher chemicals such as carb cleaner will often remove the subtle plating details. In the mean time Id take a hard look at every other component of your fuel system to find the source of the contamination. If you think its just residue from evaporated fuel try using a quality fuel stabilizer before parking it for long periods. You could also run the carbs dry before storage which sometimes helps.