07-03-14, 11:04 AM
First thing I would do is change the plugs. I had a similar problem recently, with similar circumstances. Sitting out in the rain neglected. Changed the fuel, filter, cleaned and balanced the carbs, even took the plugs out and cleaned them. All back together and still rough as a badgers arse. Put new plugs in and all perfect now. Mine hadn't been changed in about 4 years though, so they owed me nothing. 
