Well, I'm new here and this is my first post. I found this thread by searching for 'leaking carb' and might have an interesting story to share. Maybe someone will find it useful.
I have a Skyhawk GT5 66cc engine which I purchased recently and have been riding for a couple of days. Yesterday engine started to get coughs and today it turned off. I noticed that the carburator was leaking fuel. It would only leak when fuel valve was completely open.
Since the engine has gone through about 30 miles it somehow seemed unlikely that it could be caused by junk in fuel. Spark plug was also cleaned. It was even replaced with another one when I was taking the spark plug out while
defflooding the engine.
Afterwards I took apart the carburator and noticed that
mainjet was unscrewed and dropped in a bowl. Being a noob, I wondered whether it was supposed to be like that, but concluded that it wasn't. So I screewed it up, assembled everything back together and... it solved the problem. So I guess the lesson is: check everything related.