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Old 05-29-2011
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Black Smoke and Exhaust Problems
I am hauling our boat soon and I was wondering about our prop and if it is the correct size for the engine. I say this since the engine will start to blow black smoke once it reaches 2900-3000 RPM. Dave

[JED] This must be corrected, as you are limiting the useful working life of the engine. Possible reasons for black smoke -
  • prop pitch is excessive [engine is overloaded and is running too rich]
  • dirty bottom or prop
  • transmission problem
  • old fuel [very common]
  • kerosene being burned instead of diesel fuel
  • air inlet restriction
  • turbo problem [only for turbo charged engines]
  • engine cannot get enough air while running at high rpm [engine space not properly ventilated]
  • restricted intake or exhaust valves
  • improperly adjusted valves
  • restricted exhaust system
  • injection timing incorrect
  • injector problem
  • low engine compression
  • engine is not reaching correct operating temperature
I would check the simple things first, as in the list above. Did your boat always have this problem, or did it develop suddenly, or gradually?

If your fuel supply [in the boat] is more than 6 months old, and no fuel stabilizer has been added since you filled the tank, it is suspect. Most sailboat fuel tanks contain at least SOME very old [several years] fuel. The tank should be pumped dry, inspected for condition, and fresh fuel [with stabilizer] added. Also change all fuel filters.
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