Carb or fuel injected?
If you have a marvel carb.... lightly with finger tips try wiggling the bottom half of the body. After a few hundred hours of normal operation, the vibration can and will loosen the float bowl / bottom half of the carb body from the top half. Even if the screws have lock tabs and or lock wires, the threads loosen from vibration wear. It might not leak fuel on the ground but in flight they will, especially in a slip on approach. There is a SB or AD several years old on this. It is easy to check this one at every oil change when the cowl is off.
If injected, after shutdown, the fuel will heat and expand in the small lines that run to the injector bodies. The injectors have ports and fine screens that will vent the fuel & vapors under the cowl. If a shut down was just the right amount of time before start up and take off, and if your cockpit air is from the top side of the cowl, you can get a momentary fuel smell on the take off roll - but that is about the only time it would be noticed.