If your Motorcraft 2100 won't idle and only runs at high RPMs, there could be a variety of reasons. Here are some common issues to consider:
- Vacuum Leaks: The most common cause for a carbureted engine not to idle properly is a vacuum leak. Check all vacuum lines and connections. Also, check the base gasket underneath the carburetor and the intake manifold gasket.
- Idle Mixture Screws: On the front of the 2100 carburetor, there are two idle mixture screws. If these are not set correctly, it can lead to idle issues. They should be adjusted in tandem for the best idle quality. The typical procedure is to turn them in until lightly seated, then back them out 1 1/2 to 2 turns as a starting point and adjust from there for the best idle.
- Idle Speed Screw: This screw, typically located on the side of the carburetor where the throttle linkage is, adjusts the base idle speed. Ensure it's not set too high.
- Clogged Idle Circuit: If the idle circuit in the carburetor is clogged, it can prevent the engine from idling correctly. This might require a thorough cleaning of the carburetor or even a rebuild.
- Choke Setting: Ensure the choke is opening fully when the engine is warm. If the choke is stuck closed, it can cause a high idle.
- Throttle Linkage: Make sure the throttle linkage is not binding or stuck, which could prevent the throttle plates from closing fully.
- Damaged Throttle Plate: If the throttle plate is damaged or not seating properly, it can prevent the carburetor from idling correctly.
- Timing Issues: If the ignition timing is off, it can affect idle. Make sure the timing is set to specifications.
- Fuel Pressure: If the fuel pressure going to the carburetor is too high, it can cause flooding or other idle issues. Ensure your fuel pump and any regulators are working correctly.
- Float Level: Inside the carburetor, the float bowl's level can affect idle. If the float is set too high or too low, or if the float is sticking, it can cause problems.