When was the last top-end done? Carbon deposits on the piston crown and in the combustion chamber can cause detonation under a heavy load. Too hot of a heat range on the plug can also be a culprit in this. A KDX shouldn't ping with 93 octane ( as long as the gas is fresh ), as they are relatively mildly tuned engines, and they don't have extremely high compression ratios. You may also want to check the timing, too much advance can cause detonation. It has been my experience that most KDXs have slightly too much advance from the factory, and they typically benefit from retarding the timing very slightly. If the jetting is still stock, that is definitely not the cause of the pinging, as KDXs come jetted way too rich. If it has been re-jetted, a too-lean jetting condition can contribute to pinging, but I don't think I have ever seen a KDX that was too lean.:p