Unfortunately, leakage around the throttle shaft after the engine is turned off is quite common (maybe the norm?) with modern fuel.
When the engine is turned off, the fuel pump inlet check valve closes, preventing fuel from returning to the tank.
The heat from the engine now causes the fuel in the fuel line from the fuel pump to the carb to expand, thus pressurizing the fuel line to a pressure which the carburetor float cannot withstand.
Fuel from the fuel line dumps past the carburetor fuel valve into the float bowl, raising the fuel level above the main discharge nozzle.
Fuel drips out of the main discharge nozzle down onto the thottle plate. If the throttle plate is closed, it runs out the throttle shaft. If the throttle plate is cracked open, some runs out the the throttle shaft, and some runs down into the engine.
The cheapest (non-political) solution (other than non using the vehicle):
Buy the lowest octane, name-brand fuel that does not "ping" in your vehicle. This will minimize but not solve the issue.
The best solution:
Install a three way filter right at the carburetor, and run a "return line" from the "vapor tap" on the filter back to dump in the top of the fuel tank.
Jon.
