Motorcycle Repair: 1975 Honda CB 500T, smoking exhaust

Question
I am working on a 1975 Honda CB 500 T, a project to keep me busy during the long, cold winters in North Dakota. The bike had been sitting for several years prior to my purchase and has about 12k on the odo.

The bike starts hard and noticed oil does blow down the header when I ran the motor only a short time.
I performed a cold engine compression test (both plugs out, oil to level, choke and throttle wide open) after ten kicks on left and right cylinders psi reads  120  on both banks.
From what I read in the manuals the low psi would constitute a ring and valve rebuild.  Would this be your assumption as well?

Answer
Hey Mike,This bike i'm not real familiar with.In general though,the compression sounds a little low.Hard starting is a good sign of it being to low.Make sure the hard staring isn't a carb problem.If it starts easy with spraying intake with carb cleaner or starting fluid than the fuel system has a problem.Over time oil can seep past your valve stem seals getting into the combustion chamber,which isn't that big of a deal,now if it continues to smoke after five minutes or so than there is a piston and/or ring problem.I would double check what the compression ratio is supposed to be.Having the exact same compression on both cylinders is odd for a worn motor.I hope this helps a little and good luck,David