To set idle mixture screws:
1. Get the engine up to temp.
2. Shut the engine off.
3. Install a vacuum gauge to a full manifold vacuum port.
4. Turn the screws all the way in until lightly seated.
5. Next, back them out 1 full turn and restart the engine making sure the choke is completely off.
6. While at idle, back them out 1/8 turn at a time, alternating between the 2 or 4, until highest vacuum is achieved. Be sure you keep all 2 or 4 screws even.
You can also do these adjustments without a vacuum gauge. The adjustments are the same except you will adjust to highest engine RPM at idle. There is a video on performing this procedure on Holley TV.
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