The length of tubing between the clunk and where I pinch is longer than between the pinch and the carb.
It doesn't matter where you pinch the line, there is no vent so the fuel flow stops immediately. That the engine doesn't stop right away means that the fuel mixture is rich and that incoming air is picking up fuel clinging to the crankcase walls and bottom. If it was at peak or lean it will stop immediately no matter how long the line or where you pinch it.