Found a bug.
Sometimes some games don't support video modes you have forced, then you have a black screen or the game doesn't boot.
You have to reset the Wii and launch again the loader.
And with Wiiflow, when you restart it after that, you have a message like this " Please connect a USB drive in your USB port or check if your USB HDD is correctly plugged " . Very strange message because between these 2 actions, I didn't touch my USB drive.
You have to wait 10 or 20 seconds until the message gone, and the loader can run.
The loader keeps in memory the last game you have run, and if the game cannot be run with your settings, this causes a bug.
I had this bug with Twilight Princess PAL and Little King Story PAL, NTSC forced on a Japanese Wii.
sorry for my bad english.