Curt -
Given that some people who post to this forum seem to take a lot of heat, I appreciate you taking the time to respond to my question. I originally suspected the carburetor because I had read the plugs before going to the track and they all seemed about the same. While at the track, someone pointed out some smoke from the passenger's side exhaust. When I got home, I pulled all the plugs with the results I described earlier. A local mechanic suggested the carb was dumping extra fuel during hard cornering with the unaerosolized fuel flowing to the outside of the turns. That's what led to my original post.
Since then, I installed all new spark plugs, slightly lowered both the primary and secondary float levels, and dropped the primary and secondard jets by four sizes. I then drove the car about 8 miles including one full throttle pull through second gear. I pulled the #2 and #6 plugs and found the #2 blackened and #6 clean. As I did no hard cornering during this time, I concluded that the soot was likely due to
oil leakage rather than fuel. Consequently, I had a compression leak-down test done. All eight cylinders tested normally.
At this point, I don't know what is causing the soot buildup on the #2 and #3 plugs, but I have one more idea. The engine was rebuilt about 3,000 miles ago. Shortly before my last visit to the track, I switched from conventional to
synthetic oil. It is possible that the
synthetic oil is leaking past some of the rings to a greater degree than the conventional oil. My next step is to change back to conventional oil and drive it a while further. If the soot goes away, I'll know where it came from.