Carbs, Starters and Valves, oh my!

Like said , you need a good hard copy of the factory manual but for the now there is a PDF for the Kz650 B1 right here on the forum

www.kzrider.com/modules/ServiceManuals/K...Service%20Manual.pdf

Also at 6,500 ft you should be running a lower octane fuel like 87 or 85 if you can get it,
higher octane retards the combustion and is not efficient for these older bikes with the lower compression especially at higher elevations

When brand new spark plugs soon get sooty and fail to produce combustion in the cylinder, and the ignition appears to be strong with a properly timed fat healthy spark with brand new plugs, and the compression is acceptable along with proper valve clearances, and the carb is clean and properly jetted, remember to perform the clear tube test to determine the existing fuel level, because a too high fuel level can itself alone result in a quickly sooting and failing spark plug even though everything else is "perfect."

Good Fortune!