I pulled the cover on the side, and it turned out the intake valve had half slipped out of the keeper, so it would jam at the bottom, doing a good imitation of a stuck valve. Once I got the spring and keeper out the valve and guide appeared very clean and free and in good condition.
Now what I got to figure out is WHY. The valve seems a very loose fit in the spring retainer - it slides out very easily, in fact, would rather slide out than stay in place, which makes it hard to get the little disk (which Honda I think calls the valve adjuster) in place, to hold it centered. I have the opposite problem from you on the little disk - it is a pretty sloppy fit too.
Never having worked on one of these before, I have no way of knowing if this is normal, or if the spring retainer has worn abnormally so it no longer stays in place, and should be replaced.
I am getting very tempted to just put it back the way it is, and see if the thing will run and the alternator make power, before I buy any parts - wow, Honda pars are not cheap. Just the little 1-1/2" x 1-1/2" cork gasket on the inspection plate is $9, and the tiny retainers $8 or so.
The keeper was off the spring for some reason. It was too dificult to get the valve back in. I tried a couple of lite passes with 600 on the guide to no effect. I figured the valve end was hit by the keeper, brass or some of the brass. I made a couple of lite passes with a very fine file on the end of the stem. That must have take off a slight high spot as the valve fell in after that like expected.