You need at least 110psi to run a honda 600. 160 is new rebuild spec. 150 is normal. Maybe your gauge is bad. I made a leak down set with an air compressor regulator and a hose from my compression tester. Dont forget to brace the crank with 17 or 22mm wrench and if doing a leak down might loosen all valves more than normal.
Some N6 have the valve seat issue where it pounds into the head and you can never keep an adjustment.
600guru since 1981
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