Black plug indicate a rich mixture, being wet just means that your getting fuel. The gap is most likely not a cause but should be around 0.030. You need to lean the mixture. adjustment will depend on the engine speed when you are experiencing the issue. If it's not idling right you may only need to adjust the air/fuel screw inward, should be set 1 7/8 turns out. If you have one on that carb, if not the slow speed jet will need to be changed. mid to high rpm mixture is adjusted by either needle height or pilot jet/main jet size.  You opened a new ticket so I don't have the previous info. Hope that helps.

Thanks,
Scott