Sounds like you've got some dirty lead. You may need to drain your pot, clean it up and start over again.
Do you only use clean lead when pouring?
If your using wheel weights and other things like that you would be better off just to melt all that down into ingots at one time and clean the pot. Then you will have clean lead and shouldn't have a problem with it clogging. The only time mine clogs is when I'm melting down dirty lead to ingots.
Charlie