Atlas 30mm carb tuning for high elevation

New pair of Amal 30mm carbs for my Atlas coming and need to fit jets to suit 7,400' and above. Any help? Thanks in advance, Chuck.

Nope, it looks like you are on your own.
At 7000 ft above sea level, You need to keep weakening the main jet until you get the right plug colour.
Just remember, if you run the bike below the height you set it for, the main jet will then become too weak . . . . . .

Thanks Bernhard, The carbs arrived yesterday and I can say the new aluminum bodies look great. The paperwork that was in the box has some info. It says "Carburetters ex-works are set suitable for altitudes up to 3,000 feet approximately. Carburetters used constantly at altitudes 3,000 to 6,000 feet should have a reduction in main jet size of 5 percent. And thereafter for every 3,000 feet in excess of 6,000 feet altitude further reductions of 4 percent should be made". So this should get me something to start with, I think. Thanks again, Chuck.

I wouldn't worry so much about the main jet. I lived in Lake Tahoe at 6300 feet and the altitude was always a problem. If you intend to always drive the bike at that altitude and never go to lower elevations then set the carburetion for that elevation. If you want to go up and down in elevation then you need to find a solution that can be switched back and forth somewhat easily.

My solution: run the next hotter plug and perhaps open up the air screw a tad. That way, when you go down the hill, you simply install the correct plugs and close the air screw a bit. Expect to foul spark plugs more often at high altitudes. Live with it. The stock Champion N7yc is a little bit better than the NGK BP7es. Do a little research and find the next hotter plug. NGK and Champion are different in their numbering systems. The non-resistor Champions are only available on the internet. Buy several pairs.

Another variable is that you have replaceable pilot jets in the premier carbs. At your elevation, the #17 pilots (2-ring) could very well be a good choice
Descend to 3000ft. and lower and it will probably be a pig to start and run lean. This is far more important than main jets. Remember, you will ALWAYS be on the pilot jet and you will most likely NEVER be on the main. I am at sea level and the #19 pilot (3-ring) is the way to go.
Unfortunately, changing the pilot is not easy on a Norton so that variable is somewhat out of the question. By the way...see what pilot is in the carbs currently.

Carbs come with 190 mains and 17 pilots, The lowest I think I'll go is probably 6,000 or so. One of my favorite rides has elevations of over 10,000 and one pass of 11,000 took a little time to get the mikuni's on my other bikes dialed in. These are the first Amal's I've ever worked with, should be fun. Thanks for your reply.

Tuning Amals is not unlike tuning Mikunis - the increments are maybe a bit coarser, but the principles are the same.