One more.

The fuel in the line is heating up after engine shut down creating a vapor lock. Using the choke breaks the lock. This happens to a lot of engines that don't have much hot air exit area, or that don't get any wind flowing through the cowl after the engine is shut down. A simple issue that is easily cured by using the choke. If the choke is too much bother re-route the fuel line or fly without a cowl.

Something similar happens to an auto engine after shutting it down. They get hotter than they were when they were running. That's why most cars today have a cooling fan that turns on after the ignition is turned off.