Just don't put the clips in the pot. Cut them off with a hatchet or bolt cutter.
My pot is 20 years old and I have melted most types of lead known to man it that thing. The problem with wheel weights is they contain some alloys like antimony which make them harder than plumbers lead. It takes a hotter pot to work well with them and sometimes you have to do stuff like smoke or crack the mold to get them to pour well.
From what I understand there are a lot of impurities in wheel weight lead. I have purchased some lead on ebay and some of it is good some of it was horrible. OK for jigs not ok for split shots. I found a site that was linked somewhere on here that sells like 98% pig lead which is what we want for pouring lead.