take off the carbs and check the floats, see if they are perferated. i had the same problem and shook one of the floats and it was full of fuel.this would cause the bike to take on some fuel and flood the cylinders, i hope this helps. take one bowl apart at a time or else put the pieces in labeled containers, left and right carbs.i got used replacement carbs because it was cheaper at the salvage yard.the previous owner lost some seals and o rings .the float jet may not be seating either.really clean those carbs well, even when you think they are clean give them another shot of carb cleaner, thats all i can tell you now