I've done 30 km on a 1969 BSA Lightning which has just been overhauled.
The right-hand exhaust is discoloured to about halfway down the left has a slight yellow blush about what I would expect.
Ive checked the carburettors and everything looks ok jets the same and needle heights the same, floats ok, new float needles and gaskets.
It has electronic ignition and a single double wound coil.
The plug was a lighter grey than the left but not really white.
Its got me stumped