Old car guy stuff. (Both old guy and old car) 

Just because that weird fuel thingy on the top of your engine has brass screws with flat-head screw driver slots, doesn't mean you should tighten them as much as possible. 

In the image is a new "idle mixture screw" (center) smoothly machined, conical tip to allow a predictable about of fuel through a small hole when the throttle is closed. 

On either side of the new screw, are the ones originally removed.



https://image.nostr.build/60b0e442490bdcb9e4b3087d7d6ad4cfc07b96c052ef240f91b8999ff3fe36e0.jpg https://image.nostr.build/be457f504358e37b64318e996d5309f274315ac9c2b36a2738a2cc03754791b0.jpg