Compression should be 57 not 52 , so something is off , i am guessing valves not seating or lash too tight , you did not mention what the valve clearance was or what size shims you found under the cups/on top of the valve stem indicating how worn the valves are , also a couple other things to check , you mentioned cleaning the carb , that does not always confirm that the pilot jet is clear , they are inexpensive , (about $6.00) so i would recommend replacing the pilot jet as even if you can blow thru it , does not mean its clear enough to give the proper amount of fuel , i would also lift the subframe/airbox so you can see in the rear of the carb , then twist the throttle and see if you see a squirt coming from the Accelerator Pump , the squirt should be a solid stream and just barely miss the slide , it should not hit it , this will confirm the A/P is working and also that the A/P timing is correct (it is adjusted by the screw where the cable goes around the drum under the black cover , covering the throttle cables)
Also confirm that all 3 timing marks are aligned at the same time , inside the little round plug in ignition cover , at the cam the 2 lines aligned with the head (like this - - ) and inside the large round plug on the clutch side , the dot and arrowe should be aligned , this will confirm timing is correct
Report back with findings ...