Your advance mechanisms may be advancing too much. &/or too soon. Weak or a broken spring on the centrifugal advance, or faulty vacuum advance can cause that.
Try driving with the vacuum advance disconnected & see if it makes a difference.
You need less advance. Too much can cause pinging like you are referring to. Its possible the head has been cut down too much giving an excessive high compression ratio.
Don't keep driving like that, you can destroy the engine.
George
