KA Sr to KA Jr

Just purchased a used kart with a KA Sr motor. We race KA jr. Is it as simple as replacing the senior header with a junior header? Any tuning required after changing the header?

A new KA is sold with both headers and in looking through the manual there doesn’t appear to be any difference in settings. If you don’t have the manual you can see them here:

It is as easy as replacing the header and running as is. You may just need to adjust the mixture needles slightly, but nothing more than that. We’ve gone the opposite way for us, running our motors in Junior initially, and now in senior.