Questions about rough running, like it's only on one rotor 12A N/A
 

Looking at buying an rx7 with the 12A and a manual from a buddy, he says he was out driving it one day, there was a big bang and since then it runs like hammered cr@p, he thinks it's maybe only running on one rotor, I've never messed with rotaries and this seems like a solid car other than the issue with running, even before the bang he says it was pretty gutless and he put some pretty small tires on the back bevbeca he couldnt get it to spin the tires with a normal sized tire, so anyways how expensive of a fix could this be or what could be wrong here? Thought about 13B swap but all the 13b's I'm seeing are around $2000 and he's only asking$800 for the car so, anyways thanks all

check the basics first, check compression. if its ok, then there is a thing called the shutter valve which goes bad and will cause it to run on one rotor