I'm not sure what is being done wrong but I have used that pipe on my nt1 and never had a problem. I did use the xray long muffler wire, but that was because the pipe was out too far from the chassis and the regular wire didn't reach. I also don't run 65mm front tires, so that might be where to start.

If you push the pipe in closer to the chassis, it bends at the header and you don't get a flush seal, but I think he said that already.