My 2003 ktm 125 sx cuts off power when it should be reaching the powerband?

My friend rides with me all the time and he lives across town so he leaves his own yz 125 at my house, so i know the difference between the two bikes. My ktm bogs whenever it should be hitting powerband, but my friends yz hits powerband just fine. My dad and i replaced the spark plug, cleaned the air filter and really oiled it up, and cleaned the carburetor. It runs good in the low end of a gear but when you hit the mid-high end of the gear it will make a weird sound and not go any faster then before. I bought it for 1250 a month ago and it has been doing this since i got it.