Why are my distributor cap terminals burnt?

Finally had a chance to put the timing light to work. Idle is set to 650, 14 degrees advance. It held 14 degrees until 1800 RPM. At 1900-2000, I'm at 15 degrees, 2100 - 16*, 2200 - 17*. It's a little tricky doing this by myself and especially considering the timing mark is on the opposite side of the throttle lever (much easier on a small block).

Anyway, I decided to try to determine what my total was. I got 24* at 2800 RPM and it stopped advancing at that point. Why would I only get 10* mechanical advance? Am I doing something wrong here?