Pinging problem

This car runs on natural gas. From the moment it starts, it runs rough. Put your foot on the gas (any gear or neutral) and it gets worse. Put a meter on it and drove around and noticed that (trying to remember exactly) the timing at say 900 rpm's and moving at ten mph is something like 10-12-14 degrees, but step on the gas just a little and timing jumps 20-24-28 degrees and engine starts pinging bad. Now if you put the petal to the metal from here timing falls back to 10-12-14 degrees and she takes off like a rocket! But anytime and at any speed the throttle is just off idle through 2/3 open the timing is advanced ten to fifteen degrees higher than it should be (in my opinion) and it runs bad. Any ideas or comments?