Holley/Demon Carb stumble
It takes air flow thru the venturi and booster to create a pressure differential to get the fuel flowing.
At elevation, the air is less dense, so it requires a larger volume of air to create the required differential.
The smaller venturi speeds the air up and makes it more dense, which helps activate the main circuit earlier........ which should make tuning the bog out easier.......which should make it 60’ better.