[Formulajones]

Absolutely makes a difference. I deal with it all the time living at elevation and frequently driving to sea level.

Like Steve said really depends on how the carb was set up to begin with. It may have just been running a bit on the rich side up there.

Just have to try it out and see. If you're rebuilding anyway may as well get the kit from Cliff and he'll spec the parts for your combo, then you won't have to worry about whether it's been tuned previously.