Burnt Valve?

If after the 2bbl is on it and you follow all the recommended checks above, and find nothing wrong - maybe the valves need adjustment. Perhaps one of the adjusters backed off, the oem rockers use a friction adjuster, in other words no lock nut to hold the adjuster in place. Maybe that might be part of the story. worth checking after the other stuff. You can replace the friction adjusters with standard locking types btw.