[Tired Old Man]

A 400' change in elevation will not have an appreciable affect on carb tuning. If so we would forever be chasing the needle tuning for the constant altitude changes our planes fly through. The diaphragm carbs we use are generally self compensating for altitude changes of well over 2,000'. If you have the carb well tuned for your local field altitude there's really no need to fuss with it when flying at a field that's 1,500' either way of the home field. Any gains will be negligible.

There have been planes that have flown with starting density altitudes of below sea level and ended up flying above 18,000' asl without any carb adjustments. Many others frequently fly at altitudes over 12,000' that have carbs originally tuned for a base altitude of 500' or less. However, they do start out in an excellent state of tune. No further adjustments are ever made.

The trick is being accurate with the original needle settings.