[john walker's workshop]

carbon bits can fall between the valve and seat if you remove the plugs before doing the adjustment. then the valve closes on the carbon bit, you adjust the valve, and when the engine starts and the carbon blows out, you have a tight valve clearance.
you will also need the proper feeler gauge holder, because the tip of the gauge must be at 90 degrees to get under the elephant foot adjuster. you can't do it with a straight gauge, it's too flexy. some you can see, some you can't, and have to just feel it in and out.