Well, it is a long story, so I'll give you the Reader's Digest version.
I cleaned the carbs several times, and got them all set. I think the #4 plug was a victim of leaky valve seals. Oil was getting into the cylinder and burning off, once the plug got hot enough. It was running on essentially 3.5 cylinders. In August of last year, while riding home from my doctor's office, the cam chain between the head and the crankshaft snapped. Not sure if it was due to bent valves, or just the chain losing all its tension. It would have cost about $2000 in parts and labor to rebuild it. The mechanic kept finding stuff that should be replaced as we dug deeper into the engine: crank bearings, rod bearings, 2 each intake and exhaust valves, rings, seals, gaskets. Basically an engine overhaul.
So, rather than fix it, I found a local guy who was rebuilding his own DOHC 750, and sold him everything for about what I had in it. So I got back some bux, he got essentially a whole parts bike, and in January 2011 I bought a 1984 Honda VT700c. I put about $250 into it (new tank, pieces parts, and some labor to get the jellied gas out of the carbs), and I've been running it ever since.
Not sure if that answers your question or not, but that's what happened.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.