I have a 2006 WR450, with an AIS kit and the Power Now kit, which includes the power bomb header, FMF Q2 series pipe and the Power Now insert on intake side of carb. I change the pilot jet to a 48 and the main jet to 170. The AIS kit came with adjustable needle set at 3 notches from the top. It seems to back fires when I backed out of the throttle. (I was riding in the Mojave dessert, California.) The Power Now's instructions talk about "a fuel adjustment screw," I have the stock carb, but I cannot see, nor find, the fuel adjustment screw. Any suggestion on where to look for the adjustment screw? Or why it back fires?