2002 Mitsubishi Eclipse pings when I accelerate

2002 Mitsubishi Eclipse mileage: 55,335. My 2002 eclipse pings when I accelerate, especially when I climb hills. It also tends to do this when my rpm's drop after my automatic transmission switches to a higher gear such as third or fourth. I've already checked the ignition timing and it's correct, I've replaced my plugs and wires. My cylinder head was just replaced in 2005. What are some of the causes of this problem or can you give me any advice to aid me with this problem? Also, as I replaced my spark plugs, I noticed that they had carbon deposits on them thus telling me that my car is delivering more fuel than oxygen into the combustion chamber. The inside of my exhaust is black and filled with carbon as well. My dad is a mechanic, and he believes all this is caused by my valve lash adjusters that tick like crazy. When we replaced my cylinder head, I couldn't afford to buy new adjusters, so we put the old ones back in. Could the adjusters be the reason for any of my problems?