Txt camshaft

[93 marathon]

I just came in possession of a 98 txt with 295cc robins. It wasn't running with half the power of my 93 marathon (same engine), so I decided to do a valve adjustment. When I opened it up I noticed the cam looked weird. I wiped it off and it looks like someone had it out and sanded it with a grinder. First thing why would anyone do that? And second, would that small amount of the lobe taken off cause that big of power loss? Also what is the best place to buy a new one? Would a cam from a 350cc fit and make any performance difference? Last thing, since this was done to the cart, should I change the timing belt also?

Thanks in advance for any help.