I'm Also in the same boat trying to figure out sprocket sizes, also ground clearance. Gonna run a motor between 5hp and 6.5hp would like it to be quick off the start but also have good top speed, the kart I got had a small engine and a 16T shaft sprocket and 30T axel sprocket on it, I've been told that would do nothing
Yeesh. That's pretty badly pitted...

Ok well he said:
If the pitting sticks up use a 3m pneumatic spinning tool to clean it off then wire wheel again. if it is recessed pitting and smooth to touch ignore it, it will not hurt the belt at all.
Me: Ok we'll those pit that you see are down into it, so you are saying it is ok to use?
Blaz: As long as the surface feels smooth it can't hurt.
So I guess it is fine? Like the surface is not smooth because of the pits but the pits are smooth because I took a wire wheel to them, there isn't any rust in them. ???

Looks like a diff.
Looks like a diff.
Yep. And unless you're running only on pavement, you're best to eliminate it.