I'd suggest reading through this thread.
http://www.sailnet.com/forums/diesel-engine-forum/55720-yanmar-black-smoke-exhaust.html
It may have your solution or give you some ideas on which way to continue in your search for answers.
http://www.sailnet.com/forums/diesel-engine-forum/55720-yanmar-black-smoke-exhaust.html
It may have your solution or give you some ideas on which way to continue in your search for answers.