Im playing Mario Kart and it runs around 35~60 fps which settings should i use
My specs are Core 2 Q8400 4 cores 2.66Ghz clock speed, 8GB 1333mhz ddr3 ram, Radeon 6570 1 GB
You never specified which Mario Kart (Double Dash or Wii) as they can have different hardware requirements depending on certain situations. In any case, 35-60 FPS is probably to be expected given your PC. Your CPU is pretty slow as far as Dolphin is concerned.
Overclocking the CPU may help if that's an option available to you. Just be sure to read up on how to do it safely. As for settings, I suppose you could use the latest development revisions and use Asynchronous shaders. Beyond that, if you're willing to risk some instability, you can manipulate the emulated GC/Wii CPU. If you override the default speed, lowering it should make it easier on your PC to run games at higher speeds. This is potentially risky as game crashes and glitches may have a higher likelihood of occurring. As such, messing around with the emulated CPU settings is not recommended, but it is an option available to underpowered setups, just know the warnings surrounding it.
Beyond that, there's not much to do AFAIK. Your hardware just isn't fast enough for Dolphin, and generally there aren't magic settings that you can just tweak for fullspeed.