Seems like you’re getting lots of good advice, but the issue hasn’t been nailed down yet. So I’ll pile on!
Shaffer's1950 raises an excellent question about color of the spark plugs: you replied Gray / White.
Wouldn’t this indicate very hot combustion chamber burning caused by excessively Lean fuel mixture? Jetting, fuel supply, manifold or carburetor mounting air leaks, and spark plug heat range are some possibilities.
