Low compression across all cylinders

Hello everyone, my beautiful 1980 kz750 LTD h1 has below 100 psi across all cylinders. I bought the bike last may and put well over 3,000 miles on it with minimal issues. The bike has 32k+ miles, due to being a novice, I didn’t check the compression at time of purchase. I’m thinking I bought the bike with low compression and it’s finally bit the bullet. After putting oil in the cylinders the compression shot up to about 120 psi. This leads me to believe the rings are bad, I am making this post to do some brainstorming. To me it doesn’t make sense to have all sets of pistons rings to fail at the same time, I was curious if some of yall have any other ideas of what could be going on or if it could just be the rings. 

How long since the last valve clearance adjustment?  The valves tighten with mileage, and eventually all the clearance goes away, and the valves hang open.  When this happens, the valve face and seat can burn, damaging them.  Sometimes you get lucky, though, and the parts carbon up without too much damage.  

Unknown, they have not been checked under my ownership. I did ask my mechanic about the valves when the bike was running and he said it didn’t sound out of adjustment. Whatever that means lmao 

Check the valve clearance with feeler gages, not yer eeerz. 
Also, did you measure the cylinder pressure with the engine at operating temperature and the carbs removed or at least with the throttle held completely open? If no to any of those, you will get low readings.

My mechanic measured the compression and sent me videos, I’m assuming he followed the correct procedures. The bike was not able to run due to such low compression. It was strange though cause I rode the bike to the gym and it was fine, I went to go home and the bike lost spark on cylinders 1-4. I changed the coil then the bike ran but very poorly, I took it to my mechanic for further investigation and he got the low compression readings. 

Hutch03 wrote:

My mechanic measured the compression and sent me videos, I’m assuming he followed the correct procedures. The bike was not able to run due to such low compression. It was strange though cause I rode the bike to the gym and it was fine, I went to go home and the bike lost spark on cylinders 1-4. I changed the coil then the bike ran but very poorly, I took it to my mechanic for further investigation and he got the low compression readings. 

You need a new mechanic, and to do maintenance on time.

 

Not many people in my area will touch my bikes due to their age:/ . I would try to do it myself but I tend to make things worse I’ve found out lmao. I’m learning slowly 

You're at the right place for help learning to do your own maintenance. A lot of knowledge and experience here. Get yourself a Factory service manual (ebay or other market) most everything is covered there, and when you need extra direction we'll all get you through it.  You may also be able to access FSM info in the KZR archives.  Learning to do it yourself is  a lot better than relying on a mechanic with little experience in older motorcycles. 

www.kzrider.com/filebase-alias?task=down...id=1266&catid=17&m=0

That's 99.99 percent unusual for all rings and valves go south within minutes. Note all compression gauges give different readings, long hose/short hose makes a difference. Something more common to all drivetrain happened. Head lifted, camchain jumped? A better tool would be a leak-down tester.

maybe worn camchain has jumped one tooth and was the comp tested with wide open throttle?

Check cam chain tension, cam timing, valve adjustment, a tea spon of oil into the cyl., battery full charged and WOT during compression test!