hot engine pinging

[Wolfsbrg8v@aol.com (Wolfsbrg8v@aol.com)]

While my 84 8v is warming up from a cold start, there is 
good power and no pinging.  

But as it approaches/reaches fully hot, power drops off 
and moderate pinging can be heard when accelerating 
in the higher gears.

I was at first thinking this would be a spark advance problem,
but if so, why does it run ok when cold ?  Is there another
regulator of ignition advance relating to temperature, or am I
looking in the wrong place?

Leo