How to adjust the carburetor on a 1970 Plymouth Hemi 'Cuda?

When dealing with a misbehaving 1970 Plymouth Hemi 'Cuda, one of the common culprits might be an improperly adjusted carburetor. Symptoms can include rough idling, poor acceleration, or even stalling. To restore your classic car’s performance, you will need to correctly adjust the carburetor. Here is how to solve this issue:

Step 1: Locate the Carburetor

The carburetor is situated on top of the engine, centrally located between the valve covers. It is a complex piece of equipment, often made of metal, and has various screws and linkages attached to it.

Step 2: Check the Air Filter

Before making any adjustments, ensure that the air filter is clean. The air filter is housed in a round or oval housing typically positioned above the carburetor. A dirty filter can skew your carburetor adjustments.

Step 3: Identify Adjustment Screws

Examine the carburetor and find the idle mixture screws and the idle speed screw. The idle mixture screws are usually placed on the sides of the carburetor's metering block, while the idle speed screw is located near the throttle linkage.

Step 4: Warm Up the Engine

Warm up the engine to its usual operating temperature. Start the engine, let it idle for a few minutes, and ensure it reaches a typical running temperature. This is crucial because adjustments made on a cold engine will not be accurate when it warms up.

Step 5: Adjust Idle Mixture Screws

Using a flat-head screwdriver, slowly turn one of the idle mixture screws clockwise until the engine speed drops or becomes rough. Then, turn the screw counterclockwise until the engine runs smoothly again. Repeat this process for the other idle mixture screw. The aim is to achieve the smoothest idle possible, indicating optimal fuel-air mixture.

Step 6: Adjust Idle Speed Screw

Next, identify the idle speed screw, located near the throttle linkage on the driver's side of the carburetor. Turn it clockwise to increase the idle speed or counterclockwise to decrease it. Your goal is to set the idle at the manufacturer's recommended RPM, typically between 600 to 800 RPM for a 1970 Plymouth Hemi 'Cuda.

Step 7: Recheck Adjustments

After the initial adjustments, re-evaluate both the idle mixture screws and the idle speed screw to fine-tune them. Sometimes adjusting one can slightly affect the other.

Step 8: Test Drive the Vehicle

Finally, take the vehicle for a test drive to ensure it operates smoothly under different conditions. If necessary, make minor adjustments to the carburetor screws after the test drive for optimal performance.

By following these steps, you can successfully adjust the carburetor on your 1970 Plymouth Hemi 'Cuda and restore it to peak performance.