My Yamaha 1982 xj550j keeps flooding everytime it idles.

Bad luck indeed, but as @Huntchuks said, never ride with fuel contaminated oil....
Reading back quickly over your history I think you had numerous issues that caused this.
1. Your petcock - the carbs were flooding when not running? Petcock not in prime? This means your petcock is leaking, and,
2. One or more of your float valves was leaking, or not set correctly. If I recall, the Mikuni valves are held in with small clamps, and sealed with a rubber o ring - did you change these? Always assuming that the issue with the floats hanging up on the gasket wasn't the only issue, and bench set and wet set were carried out.
3. Riding with oil contaminated - I would hazzard a guess either the lifter or the valve stuck, got twatted by the piston a few times then cried enough. Feel and your ears should have told you something wasn't right, but experience is everything...

So, to fix it - new (used!) barrels, pistons and head might be ok, if you can get them cheap, otherwise look out for an engine, a good one of course.
It's a tough life sometimes, you think you've found Nirvana, only to have you kick you in the bollocks. If it's any consolation, I estimate 80% of issues with the xj is carb related...

 

Just finished reading the thread. I would guess no matter the oil contamination, the piston was already done or close to dead. When starting new project bikes, one of the first things I do is pull the plugs and take a look at each piston top with a good light. I can get an idea of what might need to be done. Rust, carbon, piston wall issues and worst of all what you have.

If you are up to it, rebuild that top end. If you have the time, tools and funding, go for it. You will gain knowledge, skill and many other mental disciplines as you move forward with the project.

Best of luck.

 

I know for a fact the leak wasn't there anymore and i put brand new oil in it! it didn't even have 20 miles on it when my blew up.

After long thought I do believe that piston was a close to death and yesterday decided to end its live and it got locked up somehow and i think the engine then skipped timing and set the valve right into the piston delivering a final blow right in the liver.

Unless the timing was right when i opened it up it looked off to me if you look at the photo below you can see that both of valves would be open at the same time, maybe it is supposed to be like that idk i can't tell until i find a service manual

I am gonna try to revive it so i'm buying the following:

Used cylinder head off ebay
New piston or used of ebay too
New set of piston rings for all the cylinders
New Head Gasket
New Spark Plug
And a new Oil filter


I really need to find a service manual please tell me if you have a pdf of one ‍‍‍

Hopefully i'll get her running back on the road again, i appreciate everyone who helped me.

 

I found a fully working 650 motor, maybe i can put it instead of the 550? but the only issue is it's probably not gonna fit or the biggest issue is that it's a shaft driven vs the chain driven, but i think i can just swap the transmission? This project is getting really interesting!!!

 

Forget the 650, nothing works.
This theory that the piston just died - it's nonsense, they don't fail unless something causes them to, and even if it did, do you think the head of the exh valve committed harri Kari in sympathy? And if the cam timing mysteriously decided to jump some teeth, all the other valves would be bent (which they might we'll be actually, depending if the motor stopped quickly or ran on for a while).
Service manuals are cheap as chips on ebay?
I would be inspecting the barrel for serious scoring, so you'll need some barrel gasket o rings as well, need to lift it to get that piston off - and drop the sump to retrieve some of the carnage...