First, be careful! Wear eye protection, gloves, long sleeves, etc.
Second, it's possible that the spout is clogged, while it's cool, run a wire in there to try to clean it out, I use a SB frame, but anything will do.
Then, once the pot is hot, and the lead melted, I'll clean it out again, in the same fashion. This normally clears any problems I have with my spout, providing the lead is melting, and the rod lifts like it should.