It rather depends on how he knows:
If the exhaust header pipe is running cool then it's probably not firing properly on that cylinder and will need sorting.
If the spark-plug on that cylinder is a little sooty then it's either not firing properly, or it's running a little rich (in which case it's not really running cool, it's running rich).
In either case it might not be a problem - if it causes no running problems, no wear and never gets any worse then it might be fine. If it is a problem then it might be a carb problem, ignition problem, or low compression (valve clearances, valve seats, rings, bore).
If it's running well then it's most likely to just be slightly uneven carb performance but on carbs that old you might make things worse if you don't know what you're doing (or what the actual problem is).
You might get away with using a ColorTune but as these only get used at fast idle with no load I think they're a bit of a red herring. You might stick it on a dyno and get the exhaust gas analysed but you'd have to tap into each header pipe separately or the cool running cylinder will be mixed in with all the others. Running with just the header pipes would mess the mixture up even more.
All in all - if it's running OK, and the spark plug isn't sooty then I'd be inclined to leave it.
arrrf.
