This is what your spark plug should look like with the engine running at wide open throttle for long enough that the cylinder head temperature has had time to stabilise.
The photo represents prolonged periods of wide open throttle between 3,500 and 3,800 rpm, using Australian (lower eastern states) 98 octane fuel and 25:1 oil/fuel ratio and a CR Machine Manufacturing low compression straight plug billet cylinder head and a Jaguar CDI using jumper settings selected for the most advanced ignition curve.
I am running a No 77 jet in the NT carburettor with atmospheric conditions at the time being an 18 degree (65 degrees Fahrenheit) day with 59% humidity and approx 120 meters elevation above sea level.
The cylinder head temperature was 140 degrees Celsius (266 degrees Fahrenheit) and the exhaust gas temperature (read from an onboard KOSO EGT sensor and gauge) was 370 degrees Celsius (700 degrees Fahrenheit).
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