When I hear someone describing an engine is pinging, the first thing that comes to mind is detonation or pre-ignition. Detonation is when the flame front in the combustion chamber is travelling too fast and is causing too much pressure on the opposite side of the chamber. When these two fronts come together it can cause a pinging noise. Pre-ignition is when the air fuel mixture ignites before the spark plug fires, usually caused from high heat in the combustion chamber. Both of these conditions are usually only heard under load and are caused by too far advanced ignition timing, low fuel octane, and lean conditions.
The first I would check is timing. Did you reuse the old balancer? The outer ring may have slipped and you are setting the timing incorrectly. The original distributor may have a broken advance spring causing the timing to advance too quickly.
The first thing I would do is retard the ignition timing and see if the condition improves, if it does, confirm top dead center is correctly marked on the balancer. Check total advance and when the timing starts to advance. If retarding the timing doesn't improve the condition then you can look else where.
Just remember trying to diagnose a noise with out hearing it is very difficult. Try the timing and let us know, then we can go frome ther.
mostly stock 74 cj5, 258, t14, d20, d44 & 30.
I'm a member of PETA.
People Eating Tasty Animals