I have a 1977 kreidler flury II Orange Moped and have had serious carburator problems for a while. I detected a crack in the upper housing of the carb and bought just the upper housing . This came with nothing but what appeared to be an ok black flat gasket. My problems were constant stalling, bogged down performance and an immense amount of gas leakage. Can any one expound on this issue and help me put this carb back together as it is detailed?