so my outlaw 525 irs has been backfiring sense new, and in doing some recent research i found out what is causing this defect. the header is not seating right with the block, the welds on top and bottom of it are interfering with the pipe from going all the way on. Polaris dealer are saying just grind it down, but that didn't work for me... at all, so i got some ultra grey gasket maker and smeared it all over where the header "meets" the block and BAM, no exhaust leak and no more back fire! hope this helps you guys! also think this applies to all KTM/Polaris bodies and engines.