What is the compression? When you say "bottom stem" do you mean the drain on the float bowl?
Also, you could have sheared off the key that mates the flywheel to the crank. Pull the left side cover and see if that flywheel is loose, or spins.
The looks to have a few little scores and a small chipI find it hard that your compression was ok with a piston like.
Now stop while your ahead...
I bet a chunk of piston skirt is also broken off of the piston.
Pull off that pipe and look in the exhaust port to see what you can see.
Could it be caused by just riding hard ?
It is the exhaust side and yes under head looks the same looks like the chunk kinda got pressed up against the inside wall of where the piston is.Is that chunk of piston missing on the exhaust side? Looks like it is,,,, also by the looks of all the carbon build up it has been a long while since rebuild/and or cheaper 2 stroke oil used. Under the cyl head look the same?
Plus with all that excessive carbon build up you can/will get a "false" compression reading.