How can I fix the engine on my Husqvarna CTH180 ride on?

Stating the obvious it is running very rich, changing the plugs only cured the symptoms not the cause, it has now blackened the plugs again and causing the missfire, i would be looking at replacing the air filter, i assume this is a Kawasaki engine? there were two different carbs the early carb had an external vented carb, this caused big problems if the breather tube from the carb ran too close to the flywheel, this caused an over pressure and made the carb flood, the later carb was internally vented to cure this, there was a retro fit kit for the carb, try first cleaning the plugs or replacing, change the air filter, and extend and re route the breather pipe from the carb well away from the flywheel

Husqvarna man
June 2010