Is it possible you have an exhaust leak between the head & ex. manifold that sounds like pinging. I can't imagine Stovebolt engine having a pinging problem like that. They only had about 6-1 compression ratio.
Does it have to run quite a while & get plenty warm before it starts or will it do it with the the engine cool?
Did it start doing it suddenly or did it slowly get worse?
Geore
