Open up 309 and setup the paths and gamecube controls. There are few versions floating around and you want the iso version for this to work) Mario Kart GP1 ( IN ISO FORMAT! if you have a different format, you have the wrong one. But the controls work in this version making it playable once you have a save slate to skip the startup)
But it needs a save slate from 309 because it give an I/O error when you boot up. Dolphin 4.0-315 (used to actually play the game. The controls are broken in 309 making it not playable so, you need 315 to play it) Dolphin 4.0-309 (Used to create a working save slate only. This is more for die hard people since this one is hard to get to work. GP2 has like 95+% of everything GP1 has so if your only interested in getting one mario game, I recommend you choose GP2 and follow the link above. This is how to get Mario Kart GP1 to work. UPDATE: you can also play GP2 using this method but the link above is still the easiest way to play GP2 I have previously posted how to play Mario Kart GP2 on Dolphin Triforce 3.0-694.