Watch a video about how this choke pull-down works:

The choke pull down on the Motorcraft 2100 2 barrel carburetor is operated by vacuum. When the engine is off, the choke valve is completely closed. If the valve stays this way when started, the engine will not run due to lack of air.

When the engine is 1st started the vacuum is at the highest point and pulls the pull down, down all the way. This opens the choke valve enough to let some air in.

If the diaphram is bad the engine may die after starting and when cold.

Watch to see if the diaphragm pulls down when you 1st start the engine. If not, replace it. Also check the vacuum passage to make sure it isn't blocked.

2100 Pull DownAdjusting the Pulldown Diaphragm

2100 Pulldown

Choke Pull Down
Adjusting Choke Plate Pull Down

  • Start engine an bring to normal operating temperature.
  • Note where the thermostat is positioned so you can put it back.
  • Loosen the thermostat and turn 90 degrees in the rich direction. You would be making the choke tighter.
  • Remove the heat tube from the choke housing.
  • Turn the fast idle adjusting screw outward one full turn.
  • Start engine and check the clearance from the lower edge of the choke valve (butterfly) and the side of the carburetor wall.
  • Compare the clearance with the specification on your rebuild instruction sheet, or from your motors manual.
  • To adjust, turn the diaphragm adjust screw located on the bottom of the diaphragm housing.
  • Turn the screw clockwise to increase the clearance.
  • Turn the screw counter clockwise to decrease the clearance.
  • Connect the heat tube.
  • Set the choke thermostat back to the original position.
  • Adjust the fast idle speed.
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