Re: 4 stroking
Other members here have said that the angled plug heads run hotter than the straight plug heads. If it is shaved as well like Greg58 thinks, then it definitely will run hot.
I doubt that you have done any damage yet. You would have seen a silvery deposit on the spark plug which is actually aluminum melting/ burning off from the piston's crown.
Also, extreme heat will eventually warp the cylinder head and cylinder and over time lead to a blown head gasket which you do not have.
A spark plug's temperature has everything to do with it's ability to keep itself clean.
Also, running a spark plug that is too cold will not give a good color imprint as it needs to be self cleaning and a too cold spark plug cannot do that.
A B7HS plug will be able to burn off the oily deposits better as it will run hotter, but not make the engine run noticeably hotter. You may even end up needing a B6HS in the end, but don't jump to that one right away. Change spark plug heat ranges one step at a time.
Adding an extra head gasket will lower the compression ratio and reduce the engine's operating temperature. Also, lowering the needle clip position one notch will add more fuel which will help cool the burn temperature but also increase the tendency for 4 stroking which is the issue at hand. I vote for an extra head gasket.
"It's a chinagirl. It's a sometimes fun little engine that often will break your heart. It's disposable.
Does not come with a fortune cookie."