Engine surging with a Motorcraft 2100 carburetor can be caused by several factors. Here are some of the most common:

Fuel-Related Issues:

• Clogged Fuel Passages: Dirt or debris can accumulate in the carburetor's internal passages, restricting fuel flow and causing surging.

• Sticking Float: A faulty float can lead to inconsistent fuel levels, causing the engine to surge.

• Worn Needle and Seat: Damage to the needle and seat can prevent proper fuel flow regulation, resulting in surging. Also dirt in the seat will cause inconsistent bowl level.

• Fuel Pump Issues: A malfunctioning fuel pump can deliver inadequate fuel pressure, causing the engine to surge. Test for 4-4.5 lbs

• Fuel Filter: The fuel filter may be dirty and/or plugged up.

  

Air-Related Issues:

• Vacuum Leaks: Leaks in hoses or gaskets connected to the carburetor can disrupt the air-fuel mixture, leading to surging. Spray carb cleaner around any gasket, or vacuum fitting. A change in RPM indicates a leak.
• Clogged Air Filter: A dirty air filter can restrict airflow, causing the engine to run lean and surge.

Ignition Issues:

• Faulty Spark Plugs: Worn or fouled spark plugs can disrupt the combustion process, causing surging.
• Ignition Coil Problems: A malfunctioning ignition coil can prevent proper ignition, leading to surging.

Other Potential Causes:

• Incorrect Carburetor Adjustment: Improper settings for the idle mixture, accelerator pump, or power valve can contribute to surging.
• Choke Issues: A sticking or improperly adjusted choke can cause surging, especially during cold starts.

Troubleshooting Steps:

1. Visual Inspection: Check for any visible damage, loose connections, or debris in the carburetor.
2. Clean Carburetor: Remove and clean the carburetor thoroughly, paying attention to jets, passages, and the choke mechanism.
3. Inspect Fuel System: Check the fuel filter, lines, and pump for any issues.