They'll partly compensate for elevation gain -- the vent in the fuel bowl isn't just to let fuel pour out, it's also an air intake for the emulsion tubes, and air pressure affects what the tubes do. BTW, your air cleaners should clean the air to that vent as well as the carb throats -- some people use foam socks that don't do that; really pretty useless.

Anyway, tuning really varies from engine to engine, so forget about where they came from. It's really good they run presentably enough to give you a starting point.