They'll probably work if your firmware is 4.5 or less (lots of flashcarts got blocked after this).
Different DS flashcarts got blocked at different firmwares on the 3DS. Installing bluecardfix will erase the block list, so as long as the flashcart worked on SOME firmware long ago, you can make it work. It won't work if the flashcart never worked on the 3DS at 1.0.