Black Smoke at High Speed

  • This could be caused by the power valve remaining open too much. The economizer cover could be warped allowing vacuum to escape.
  • A stuck power valve stem would cause the same problem.
  • Make sure the choke valve is fully open when the engine is at operating temperature. It could be out of adjustment, bad thermostat, or bad choke spring.
  • Make sure the discharge check ball is clean and loose.
Watch a video about the economizer diaphragm and power circuit.

Economizer Diaphragm Cover

Power Circuit

Vacuum Port to Economizer Diaphragm
1904 Economizer Diaphragm
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