[gitsum]

The higher the elevation the less fuel the engine needs because the air is less dense.

If you significantly open up the airbox and exhaust, you will have to retune the carb.

This means adjusting the air/fuel screw, raising the needle jet a notch or two (or using shims), and going to a larger main jet. There are plenty of tutorials online that will guide you through the process.

Be prepared for a lot of trial and error, it is the only way to make sure the carb it tuned optimally.

Since you got the old carb apart, it might be easier to clean it up and try using that first.