1982 KZ750H-2 compression

checked compression all 4 were between 82 to 90 put oil in went up to 120. Do i need to rebuild? Just rings? not sure what to do and oh yeah the head is leaking lil oil needs gasket

Maybe.
Low compression numbers can also be caused by burnt valves, valves with carbon buildup on the seating area, or even lack of valve clearance at the cam. Wonky numbers can also be had by not holding the throttle open during the test.

How long since your last valve adjust?

When you check compression you should the engine warmed up to normal operating temperature; a fully charged battery; ALL spark plugs removed; and the throttle fully open. Checking compression on a cold engine is a problem because the pistons are actually tapered some and need to expand near the tops to seal well enough for an accurate reading.

I would be careful about placing too much importance on the numbers after adding oil to the cylinders. Even a very small amount of oil added to a cylinder can make a big difference in the compression readings. I have seen more than one person advocate adding "about a teaspoon" of oil to each cylinder when doing a "wet" compression test. That may not sound like much oil to many folks, but a teaspoon is actually right around 5cc, and that is a lot. As an example of how little oil it takes to change the compression ratio I offer the following diagram. It uses a hypothetical cylinder with a total volume (cylinder & head) of 100cc and a dry compression ratio of 10:1. Even a mere 1cc of oil added changes things quite a bit, so if different amounts of oil were added to different cylinders one can see that the compression ratios might vary a lot. This example is not precise and is not any specific engine and it doesn't take into account oil that may seep past the rings, etc. It only is meant to demonstrate in very general terms how adding oil can change compression ratios. You can see how quickly the compression ratio jumps as oil is added to the cylinder. Ed

I'll add that it's a waste of time performing a compression check unless you check the valve clearances first. Valve clearance shrinks with mileage and not adjusting the valves will lead to burned valves and bad compression.

+1 If the valves are not closing all the way because of inadequate clearance the compression will be low. Ed