This is very similar to what happened to me. Fuel boiled out of the bowl of my stock 2 barrel and ignited on a hot restart. I wrote this up, along with my solution, in the TE/AE newsletter a few months back.
The fuel will boil at a temp well below the underhood temp when stopping after a hot run on a hot day. I installed a drain tube on my carb bowl vent so that any fluid that is forced out goes straight to the ground.