HELP! sound like my KZ650 is about to explode

Hi everyone, I'm new here but the cite looks like a great resource. I bought an 81 kz650 last month with 21k miles. it ran pretty good when i got it. I let it sit for about a month while i painted it then started it today and it had a bad tick, the tick turned into a bad knock after running it for about 3 mins...then it ran great with no noise for about 1 minute then the knock returned(i feel like that piece of information is important). It starts fine and sounds like the noise is coming from the top end. I'm thinking somehow it isn't getting oil to the head which is weird since it has a mechanical oil pump. I'm thinking it could be oil pump/clogged oil journal, or valves or timing chain tensioner? but what is more likely to randomly develop from sitting a month? also cylinder 2 isn't firing(pulled the plug and it ran the same) but it wasn't firing when it ran "normal" for 30 seconds either so i think that is an unrelated carb issue. it starts right up so i don't think it jumped time, and it isn't smoking but it sounds terrible. I'm guessing all i can do it pull the valve cover/ tt tensioner, and oil pump and see if I notice anything unusual. i think i might be able to save the motor if i can find and fix the problem. has anyone ever experienced anything like this? also if anyone has a link to a downloadable service manual that would be greatly appreciated.

Check to see if you have compression on the non firing cylinder, perhaps a valve has stuck open a bit.

Welcome.

Is the oil level OK?
May be just cam chain noise your hearing.
Those later model 650 cam chain tensioners tend to not work so well over time.
I haven't dealt with them, but there have been other posts about the automatic cam chain tensioners in the past, either here, or at the 650 forums, link in my signature.
Check it, make sure it's working as designed.
Some have swapped to the early manual type of cam chain tensioner, or bought a new manual one like what Ape sells.

Get yourself a service manual if you haven't already.
Factory Service Manual (FSM) for your bike's year and model is best.

How do you know the cylinder wasn't firing when it ran normal for 30 seconds? maybe you have a spark problem? Could be that carb plugged or a spark problem. If that cylinder isn't running it probably would sound pretty bad. I would think some gunk could have caused a problem in the carb or a loose spark plug connection.