Why does a 215 pump retard timing?
 

I've seen posts where the 215 pumps retard the injection timing at higher rpms. Why would they design it that way? Wouldn't you want to advance the timing at higher rpms? Isn't that just inherant of any reciprocating engine, to advance the ignition point as piston speeds increase?

Just curious.

For emissions. Lots of timing is great for making power not so much for a clean exhaust.

I can and do understand that is the reason for having retarded(to an extent) timing overall, but why only on the topend? Wouldn't retarded/advanced timing on the lower rpms also account for emmissions?