Overheating can cause preignition.. Preignition can cause overheating.. Preignition is the pings you hear.. there are things besides timing that can cause preignition.
But the question is exactly what's causing it to overheat? lack of cooling air? a lean air/fuel mixture? exhaust restrictions?
Do some searching on the net .. "overheating + 2-stroke + engine + causes" or similar..