I have a 2006 WR 450. Put on a Power Bomb header with a Q-4 exhaust. I live in Michigan so the elevation is right around sea level. This is how I re- jetted the carb. 172 main, 52 pilot, jet needle 3rd. position from the top and the fuel air screw is 1.5 turns out. Every time I get off the gas it pops like crazy out the back of the exhaust. I have taken the carb off and re-jetted 6 times to try and correct and no luck. I been on the phone with FMF every night after work trying to come up with solutions. I have had 4 other FMF systems on different bikes and quads and there has never been an issue. The funny thing is the bike starts right up, and idles perfectly. When you ride it the difference is like night and day compared to the stock system. The bike pulls harder and is a lot quicker. Just back fires and pops when you back off the gas. Any one have a problem like this? Any suggestions would be greatly appreciated.