My Wii is firmware 3.1j with only backup launcher 0.3g (no modchip). However, some new games (such as "Mario Power Tennis" ) seem require 3.2j firmware.
In this article, I know there is a way to downgrade from 3.3j or 3.4j to 3.2j. However, the Nintendo release 4.0 firmware which make 3.2 to...