well. it must of been making some power to reach the limit of the z32 afm.
to much fuel can cause pinging. not directly, but by carbon buildup in the cylinders. this glows and causes pinging. not detonation.
this is a pretty obviouse question but there isnt any air leaks is there?
also worth checking is the timing. if the cas hasnt been done up tightly it can move and the timing can change.