Dar Zeelon ,,,, I think you nailed it. I had ordered a couple A5 plugs and ran them a few weeks ago. The detonation at mid-range went away and I was also able to lean out the mix quite a bit. But I tried some higher nitro/oil fuel "PowerMaster 20/20" and in the process installed an 8plug again.
Next time I use the engine I'll go with the A5 and a normal 10 or 15% 2 stroke fuel.

No offence intended here,, but I just gotta remark on the two replies that offered zero help and seemed ,,, well,,, almost rude.
Why do you care how often someone checks their equipment ? Removing the head and backplate are the only way to see how things look inside. I use to be a fly and forget it type until it hit me in the pocket book a few times.
I promise that my next engine you pay for will never even get the glow plug checked.