[garygroves]

Eyebbober: If I read your inquiry correcly, you are asking about what causes the black smoke in the first place - if not, please forginve the reponse. As earlier stated you might need to adjust the valves. Most engine black smoke is from lugging the engine, either from over-propping or (most cases) dirty bottoms. Engines don''t like to try and push a boat that''s covered with a shag rug instead of a clean bottom. You could also have a problem with a prop covered in barnacles. Check these out. If not those, then dirty air filter or an exhaust hose that''s partially blocked will also cause dirty exhaust.