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My Av started pinging yesterday. I was driving down the highway moving out to pass; full throttle or even 3/4 throttle it went nuts. Pinging like crazy. When I got home I happened to notice that the tailpipe was black with soot. I know that after a lot of highway driving (almost 400 miles in total) a sooty black tailpipe is a sign of running too rich. Would running rich like this cause the pinging? I would not think so, I think running too lean would be one of many things that cause pinging. Also there is no mechanical way to advance the timing. Is there?
Could the rich fuel mixture have caused a build up of carbon on the piston thus raising the compression ratio? If so is there any additive that will remove the carbon? I the old days I would just drop some walnut shells down the carburetor (anyone remember those?) to remove the carbon and adjust the timing to eliminate the ping. Does anyone have any ideas? By the way I have 50,000 miles on my Av.
Interested in hearing the answers... mine is pinging a bit under load now, but also noticed a new "tic" at idle, and tailpipe is noticibly darker as well.

P.S. This seems to have coincided with my last oil change. Level is OK, but could oil quality cause this?