Motorcycle Repair: Honda 600 cc Mixture Adjustment, air fuel mixture, cross country trip

Question
My son is 1500 miles away on a cross country trip on his 1994 Honda Silver Shadow 600 cc motorcycle. At high altitudes it is putting out black smoke but not burning oil. How can I verbally describe where to find the air/fuel mixture screw(s) and how much of a turn should he try? Which direction should he turn to make it more lean, clockwise?

Answer
The air fuel mixture screws only control the fuel at idle and just off idle so that won't help much.  Normally, it takes a change in jets to compensate for high altitude. I'm surprised that the bike is having this trouble.  Hondas can usually handle some altitude without having too much trouble. I rode over the pass in Colorado at 11,500 ft without any trouble a couple of years ago.  My hydraulic clutch quit working about 8000 ft which was interesting. Anyway there's not much that can be done other that getting to lower altitudes.  

If I were really in a pinch, I'd take the air filter out and leave the air box open as much as I could.  This would only work if I wasn't on gravel roads. At least, it will work for a while until I could get to lower altitudes.  

Regards
Rich