Why are my distributor cap terminals burnt?

The springs that are currently in it are blue springs, but the distributor came with heavier and lighter springs, along with charts that show the curve if I used various combinations. The instructions stated that the distributor has mechanical advance of 22-24 degrees.

Unfortunately, I didn't build the engine and the guy I bought the car from didn't have much documentation regarding the components. I measured lift when I sent the heads in so that they could order the correct springs, and if I recall correctly, the lift was .447, although I didn't measure duration. I remember being surprised by the lift, since I was expecting a little more. So to answer your question, I don't think the engine has been hot rodded much.