i'll give प्रॉप्स 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 आप connect. If आप 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. आप 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 आप get a bad server from a far away country. When this happened, I was really angry.