For years I have had BLACK SMOKE coming out of my Yanmar SB8 diesel engine exhaust.I change the injector, mixing elbow, fuel and filter. I tried everything.I rebuilt the engine. The only thing I did not try was a new muffler and exhaust hose. I installed a new exhaust system and NO MORE BLACK SMOKE. The old muffler was clogged and the rubber hose would collapes and restrict the flow of water and I guess overload the engine. I hope this helps someone this drove me nuts for years.