[snazzypig]

Just looked at your album. Really nice looking bus. One of my first jobs was at the Greyhound Depot in Billings Montana in 1965. Some of the smaller bus lines that made stops there were still using that type bus. Beautiful streamlined styling.
Looking at the combustion chambers on the head, maybe the one that was carboned up had weak ignition, or maybe it had to do with the valves out of adjustment?