78 kz1000ltd weird back pressure in oil system?

Ok, looking at some images online. The send port includes an adapter block that bolts into the upper case, rerouting the oil in the gallery to the cooler and back, and then up to the top end? Mine has this adapter.

I should be able to get to the shop after work, get some pics, and tear into some stuff.

This might help.
Steve
kzrider.com/forum/2-engine/600430-zx7-z1-oil-cooler

Should be like this pic.
One hose out to cooler ( the lower one in the pic) and the other back to the main gallery ( upper hose).
Neither of these are capped off as stock.

Here are some more detailed pics of the oil cooler line flow routing.

Zed1015 and scirocco thanks for those. This is exactly the set up I have. Gonna try some pics.

So still not sure why it could be blowing the o ring out. Could this be caused by lack of crankcase breathing?

I edited your pictures for you to open them up.
Next time hit the insert all button before submitting .

I still cant see your fitting at the block very well. But something looks fishy.
How about this .
Pull a oil line at the cooler and crank motor to see if you get oil flow , and from which side.
Next pull your fitting loose from block and check for blockage from debris / swelled hoses / and inserted plugs .
Im not kidding about a threaded in plug as WE have seen this done before.
I still believe you have a simple problem with a simple fix , but be patient and with your cooperation
we will get you sorted out
Dave

Just for testing the oil flow i would made direct loop oil line and see if your back pressure happens again.

Ok, here is what I did today....first I pulled the main gallery plug above the points cover. Oil film was present. Then I pulled the return hose off the cooler and blew compressed air. A little residual oil and air flowed freely into the main gallery. Then I pulled the input hose off the cooler and blew through. Air and oil flowed freely. Same with the hose from the pressure switch to the cooler.
Then I pulled apart the crankcase breather. I saw nothing abnormal here. I could see a bit of transmission and it was well oiled.
Then I pulled the oil filter. All was normal except the blown out oring...but is the filter bolt supposed to have a spring and check to act as a filter bypass? Like a honda? Well parts fiche does not show this and mine does not have anything.
Finally I removed the cooler adapter that returns oil to the main gallery. Perfectly clean and no obstructions. I tried to get the pressure switch send adapter off without removing carbs but couldn't get it. And I know oil went way past here anyway and now that I think back, I went all through these parts about a year ago before I installed the carbs.

Oh yeah, I blew air into the pressure switch adapter and could feel it coming out where the filter seats. So still stumped....questions
1. Relief valve is in the pump?
2. Could this just be a bad filter? And something wrong with the reluef?
3. My hose to and from the cooler is 3/8...maybe too small, but could that cause problems like this?

Pics

More pics

Just had another thought...
My filter bolt seems too long. Could it be bottoming before the cover gets full tight?