CFmoto 650 Pair Valve

I've just fitted an aftermarket exhaust to my Hartford (CFmoto), its just a cheap slip on which sounds fantastic, the only thing is I'm am getting alot of pops and bangs coming from the exhaust, to the point that it shoots out fire.

I read on the internet that the Kawasaki ER6N/ER6F also suffer from this and people block up the pair valve. I tried this on mine tonight, but found out that we don't seem to have that valve like the Kawasaki does. As anyone looked into this problem?