I was watching some youtube vids on adjusting the valves on mower engines. I saw one guy that just rotated the engine until he saw the exhaust valve go fully open and then adjusted the intake and then did the reverse intake fully open and adjusted the exhaust. my manual for the motor says to find tdc on compression stroke and then adjust both. It would be easier to do the fully open method that the guy did in the video (no disassembly to see timing) and seems to be ok in my limited experience with it - what do you guys think>>
Both methods are correct.
The first method gets used when you do not know what the cam grind is because by doing it this way you can not get the timing wrong.
Way back in the old days it was common to grind cams so that the closure speed of the valve was slowed down by the cam.
They are called quietening ramps and were very common on motorcycles to make them mechanicaly quiet at idle
BSA used a grind like that from 1910 till 1966 on some models and on all their stationary motors till they sold that side to Villiers.
These cams had to be adjusted using the opposites method.
OTOH engine makers now tell us where is the first place they both of the cams are on their base circles ( maximum clearence ) and past anything like a quietning ramp or a decompression hump.
This is why B & S say to go 1/4" past tdc to avoid any chance of a bad adjstment due to the decompression ramp on the inlet.