Before I even did the compression test or messed with valve adjustment, I think I would try to eliminate the possibility of a spark issue.
If you have one of those little inline spark testers, they work great. Inspect the inside of the cap and make sure that contact looks exactly like the others. If that checks out Ok, see about the plug wire. Visually inspect it. You could also they swapping the wire from the misfiring cylinder to a different cylinder. See if the misfire follows the wire.
