Burnt Distributor Cap Why?

[csdineley]

Ok, So I just finished rebuilding my quadrajet the other day. I also replaced the rusty old gas tank and filter which lead to the carb rebuild. Anyways got it all back together. Started test driving and tuning the carb. Everything went great. Came back home and parked the truck. Later that night I went to fire it up and nothing. After some troubleshooting I found I had no spark. Today I pulled the cap, and the button in the center looks burnt and the rotor is discolored and little. Replaced them with a spare I had laying around. Fired right up. So I wondering what could cause this???

P.s Distributor is one of those cheap skip white hei units. About a year old.