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
Vacuum Port to Economizer Diaphragm