Motorcraft 2100 Choke Circuit

This video demonstrates how the choke system works and what it looks like assembled. This is a must see if you are trying to diagnose choke problems.
How does the Motorcraft 2100 Choke System Work?


Motorcraft 2100 Choke CircuitThe original hot air choke uses a metal spring to move the choke from closed to open position. Actually the thermostat is wound tight against the choke shaft closing the choke. Hot air is brought up from the exhaust manifold to the choke housing through a hot air tube. A small vacuum port feeds vacuum from the intake up through the carburetor and into the choke housing, which helps draw the hot air up through the hot air tube. As the choke thermostat heats up, the spring unwinds letting tension off of the choke shaft and the choke valve opens.

The choke piston is used to slightly open the choke valve when tromping on the gas while the engine is cold and the choke is closed. This piston does not use any seals, or O rings and needs to glide smoothly.









Convert your hot air choke to an electric choke:


Fast Idle Cam Adjustment
Motorcraft 2100 Choke LinkageMotorcraft 2100 Choke Linkage
Motorcraft 2100 Choke Linkage

Diagnosing 2100 Choke Problems

The choke system on the Motorcraft 2100 carburetor is crucial for cold starts and proper engine operation during the warm-up period. If you're having issues with cold starts or unstable engine operation shortly after starting, the choke could be at fault. Here's a step-by-step guide to diagnose Motorcraft 2100 choke problems:

  1. Visual Inspection:

    • Check the choke assembly for any obvious signs of damage, such as broken or disconnected linkages.
    • Ensure that the choke plate (or butterfly valve) opens and closes smoothly.
  2. Check the Choke's Initial Position:

    • Before starting the engine on a cold day, remove the air cleaner and observe the choke plate. It should be in a mostly closed position. If it's fully open, the choke isn't engaging as it should.
  3. Manual Operation:

    • With the engine off, manually move the choke plate. It should move freely without any obstructions.
    • As you rev the engine, the choke plate should gradually open. If it doesn't, the automatic choke mechanism might be faulty.
  4. Choke Pull-Off (Vacuum Break):

    • The choke pull-off ensures the choke opens slightly upon startup to prevent over-choking.
    • Disconnect the vacuum hose from the pull-off diaphragm.
    • Start the engine and feel for vacuum at the hose. If there's no vacuum, you might have a vacuum leak or blockage somewhere.
    • If there's vacuum, the diaphragm might be faulty. To check, apply vacuum using a hand-held vacuum pump. If the diaphragm doesn't retract, it's faulty and needs to be replaced.
  5. Electric Choke (if equipped):

    • Many 2100s have been retrofitted with an electric choke. If yours has one, check the wiring and connectors to ensure they're in good condition.
    • With the key in the "ON" position (but engine off), the electric choke's coil should be getting power. Use a test light or multimeter to confirm this.
    • If it's not getting power, check for blown fuses, damaged wires, or faulty connections.
  6. Bimetallic Spring:

    • For non-electric chokes, the choke is controlled by a bimetallic spring in the choke housing. As this spring heats up, it expands and opens the choke.
    • Ensure the spring is correctly connected and not damaged.
    • The housing often has a hot air inlet tube connected to the exhaust manifold. Ensure this tube isn't blocked or damaged, as it provides the necessary heat to the spring.
  7. Fast Idle Cam and Fast Idle Screw:

    • The fast idle cam and screw help maintain a higher RPM during choke operation.
    • Ensure the cam is rotating freely and the screw is adjusted correctly.
  8. Linkages and Mounting:

    • Ensure all linkages are free of dirt, debris, and old grease that can restrict movement. Clean and lubricate as necessary.
    • Ensure the choke housing and mechanism are securely mounted.
  9. Engine Factors:

    • Sometimes, the problem isn't with the choke itself. Issues like weak spark, low compression, or other engine factors can mimic choke problems.
  10. Adjustment:

  • If everything seems in order but the choke isn't functioning correctly, it might be out of adjustment. Follow the manufacturer's procedures or consult a service manual for correct adjustment procedures.

After identifying the problem, you might need to replace or adjust the problematic component to ensure proper choke operation.


Motorcraft 2100 Choke

Motorcraft 2100 Choke
Motorcraft 2100 Choke
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