Secondary air injection system.

I just found out that vacuum valve on top of engine is letting air in exhaust system, not inside engine block.
Is there system letting air in engine block?
PCV system?

Well, it should have a breather tube to let out any blowby. Not sure if it has a valve or not, neither my KZ nor my GPz had one, but they did have baffling to prevent oil splashing out.
Not sure what you are referring to AFA you exhaust, though.

You can just block off the ports on the top of thevalve cover, or just connect a hose from one to the other.

Then block off the small vacuum lines going to that vacuum diaphragm.