Even simpler version is to pull both plugs.
- Bring the engine up to TDC on the side you're doing, (I stick a dowel or a #3 Phillips down the hole and rotate the engine to be sure it is at TDC) then be sure there is slack in both the intake and exhaust rockers. That way you know you're on the top of the compression stroke, not the exhaust stroke.
- Next: back off the adjuster and carefully look at the top of the valve stem itself. If there is a divot there made by the adjuster screw, you'll never get accurate adjustment. But you can guess and snug up the adjuster slightly from where the feeler gauge says you're on and hope for the best.
- If it were me, I'd completely remove each adjuster and look at the end that contacts the valve. These are similar if not the same as those that are/were used on lots of Yamahas, from the XS650 to others. They are hard coated on the valve end, and after the coating wears through, the surface flakes off/pits and that causes endless adjustment problems. If any are pitted, replace all four.
- Usually, the adjusters are pitted and there's a divot on the valve, but unless the valve divot is really deep, setting the clearance to the minimum is usually fine. The valves on this era engine tend to close up as the valves beat themselves into the head.
- Another thing that causes continuously variable valve timing on these is worn rocker shafts. With the adjuster out, see if you can feel any slop. It is hard, but "twisting" the rocker, for lack of a better term, tends to allow it to show up. There is of course some play, but not sloppy slam-bang loose.
Good luck. If I had to guess, I'd say your tappet screws are pitted, and that's the problem.
Even tho In our super mild winter's I am too much of a baby to ride. lol
