Slow motion in SSBB

Hi. When I play SSBB, the game for some reason goes into slow motion, the emulator running at about 70%, about 2 minutes into the game running. The game runs perfectly up until this point - 100% at 60fps. This is incredibly frustrating, and I can't find a fix online, everyone seems to have slow motion problems all of the time due to a lack of computing power, however mine seemingly goes into slow motion at a set time. Any help would be much appreciated

Thanks in advance