i'll give complimenten to anyone who anwser this question:y does mario kart wii disconnects u from a online race i wonder why cuz it lowers my points :(

depends how u connect. If u use DHCP from your router, there may be blocked ports. I know some games need ports forwarded to the console's IP. Try setting a static IP and placing it outside your firewall (DMZ). When doing this, make sure to program in the DNS servers for your ISP. u can obtain those from your router's settings. I had this same issue, and once I added in the DNS's, it all worked flawlessly.

Idk sometimes the person that has the main connection leaves in the middle of a race and everyone gets disconnected?

I think

usually when i play when im crushing the other guy he turns the game off and im disconnected

It can happen when u get a bad server from a far away country. When this happened, I was really angry.