My car has dual down draft Webers and the rear carb idle mixture screws leans out over a period of about 1,000 miles. Last night I traced a stumble down to this mixture screw going from 1 1/2 turns down to 1/2 turn. This is the second time I've seen this on this carb.

Does anyone have a fix?

Try using a mild form of lock-tite or better yet, a dab of silicon, or caulking, etc.

Do not use a glue.

The spring under the head is supposed to keep the tension. Its worn out or broken. Replace the spring, or add a washer to increase the pre-load.