There is sufficient fuel in the line between the tank's clunk and the carb. The fuel pressure in the tank will remain unchanged as a function of exhaust pressure. An example might help. While on the starting bench, with the throttle wide open, the engine will continue to run for several seconds after I pinch the fuel line closed between the firewall and the high speed needle. The length of tubing between the clunk and where I pinch is longer than between the pinch and the carb.

Hope this makes sense.

Some day when I can call myself an experienced flier I will use good throttle control which means I will throttle back after initiating the down line which, in this case, will reduce the fuel demand and allow the engine to run longer yet.