everything I read says to back off if I hear the "ping" while timing my car. What is the "ping" is it like a small backfire? A couple times of the car firing normally and then a little "pop" in the firing?

 

you'll hear pinging under a load, not at idle.

 

If you have a quiet exhaust, you'll hear it while driving and flooring it. With a loud exhaust, you may never hear it.
It's basically knocking, a precurser to a misfire, but not a backfire. I've heard it described as BBs rattling around.

 

i agree, if it does this at idle, i don't think it is timing related (when I took autoshop back in the day, i was told to tune until slight ping at full load and back off a degree or two, as opposed to just tuning to spec)

 

Pinging sounds like a rattle noise, much like a paint can when you shake it when the engine is accelerated. It is caused by the flame front in the cylinder exploding - typically related to too much timing, carbon deposits in the cylinders or just crap gas.