By the time you go to start the engine, cold starting, all the fuel that ran down the manifold has evaporated. Thats why it will cold start and not hot start.
A few of the problems that can cause this,
1- pressure in fuel tank builds and can force fuel out ( unlikely your problem )
2- fuel pump making more pressure then the float can handle ( possible )
3- float level to high ( possible )
4- leaking fuel well ( unlikely )
5- float partially full of fuel ( see #3 )
6- dirt or nick in needle or seat ( possible )
7- heat soak causing fuel pressure to rise and over power float ( possible )
