If this is truly the "fix" (and sounds like it evidently IS), then it is the absolutely best-kept-secret in the airplane gas-motor world. I've read the thread about popoff pressure, and all the Walbro testing and "calibration" info....

Do we all believe that this problem is just now surfacing after a few decades of Walbro carbs in gas planes?

Is there something else that maybe is being compensated for by making this pop-off adjustment?