How to adjust the carburetor on a 1967 Shelby GT500?

Adjusting the carburetor on a 1967 Shelby GT500 can be crucial for ensuring optimal engine performance and fuel efficiency. Signs that your carburetor needs adjustment include rough idling, stalling, trouble starting, or poor fuel economy. Here's how to solve this issue:

Step 1: Prepare the Vehicle

To start, park your Shelby GT500 on a level surface and apply the emergency brake. Ensure the engine is turned off and cooled down to avoid burns or other injuries. Open the hood by releasing the latch inside the car and then lifting the hood from the center front edge.

Step 2: Locate the Carburetor

The carburetor is located on top of the engine, centered between the valve covers. It typically has a large, round air cleaner assembly on top. Remove this air cleaner by unscrewing the wing nut in the center and lifting the entire assembly off.

Step 3: Identify the Adjustment Screws

You'll find two primary adjustment screws on the front of the carburetor: the idle mixture screws and the idle speed screw. The idle mixture screws are small, often brass-colored, and located on both sides of the carburetor's base. The idle speed screw is usually more centrally located, near the throttle linkage, and is often a larger, sometimes slotted, screw.

Step 4: Adjust the Idle Mixture Screws

Turn on the engine and let it warm up to its operating temperature. Using a flathead screwdriver, gently turn each idle mixture screw clockwise until it lightly seats. Be careful not to overtighten, as this can damage the screw and the carburetor.

Next, turn each screw counterclockwise 1.5 turns to set a baseline. Slowly turn one idle mixture screw clockwise until the engine's RPM begins to drop, then back it off (counterclockwise) one-quarter turn. Repeat this process with the other idle mixture screw.

Step 5: Adjust the Idle Speed Screw

Locate the idle speed screw near the throttle linkage. Turn this screw clockwise to increase the engine's idle speed and counterclockwise to decrease it. Adjust until the engine idles smoothly at the manufacturer's recommended RPM, which is typically around 600-800 RPM for a 1967 Shelby GT500.

Step 6: Test and Fine-Tune

Once adjustments are made, test the engine response by revving it lightly and observing its behavior. Ensure there is no hesitation or stalling. If necessary, make minor adjustments to the mixture screws and idle speed screw until the engine runs smoothly and efficiently.

Step 7: Reassemble and Test Drive

After completing the adjustments, reattach the air cleaner assembly by placing it back on the carburetor and securing the wing nut. Close the hood securely. Take your GT500 for a short test drive to ensure the adjustments have improved performance.

By following these steps, you should be able to adjust the carburetor of your 1967 Shelby GT500 effectively. This will help maintain its classic performance and ensure a smoother driving experience.