ORIGINAL: flhyr
Blow by? Does it look like dark blob that runs up and down only a portion of the cyclinder?
As you look down from the top with the engine carb facing you, there is a dark patch at 11 o'clock that runs from the inside top of the cyclinder down. Everywhere else its relatively clean.
the ring is also dirty right there, everywhere else is clean.
Is this the blow by?
Yes!
There may be a little where the ring gap is, but shouldn't be a whole "patch"
You might try to take the piston out, and clean the groove that the ring rides in. Sometimes if dirt or carbon builds up in ring, it can allow for blowby. I.e. loss of compression.
If you had an airleak like was suggested, you'd know it. Shimming the head would not fix the problem of overheating due to an airleak.
I'd clean the ring groove really well, put it back together with the ring gap in a different location, and try it again.
You should also be able to look at your head shims to see if gas is getting past them. You'll know it when you see it. I'd put my money leakage past the ring, before I put it on a "warped piston"