Hmm interesting ideaGenerally if there is coolant in the cylinders the plugs will look clean from the steam.
Yes there is coolant in the intake manifolds. Pretty rare leak path except to the outside via a rotted core plug.
Pressure test the cooling system to locate any leaks.
Helps to know what bike. Carbs + 3 cyl a side I would say GL1500, but the year might help.