Having a problem with my YFZ450. I just installed a WB aluminun pro full system. Rejetted to a 168 main jet 145 pilot and #4 position on the needle. When I open the throttle fast in neutral the quad backfires and stalls. I removed the air box lid and added a WB air filter. And hint on what could cure the problem? Appling the throttle slowly, bike works perfect. Also idles perfect. only quick snaps of the throttle.