I've seen this forever in mine. As the weather gets colder, one will need more prime prior to cranking if you want it to fire off after a couple blades. At idle, so little air is flowing up the induction tubes that it will not pull the extra fuel up hill. Additionally, as someone else posted, the fuel in the flow distributor and lines dumps into the engine once it is shutdown. If you are not running a purge valve, there will be additional fuel which might boil up from the servo and connecting hose.
I drilled a hole in the bottom of the FAB, inside the aft end of the filter, to allow the goo to drain. I glued a fitting on the bottom side of this hole, onto which I have a hose attached to dump the stuff behind the cowl aft end.
5 seconds with the throttle at idle will not be enough to start my engine without a fair bit of cranking, btw (AFP system).