my buddy crashed my bike a few weeks and bent the header pipe so i bought a used pc system off ebay and put it on. The tempurature dropped a lot and it is about 15-35 degrees out now and when it was last running correctly it was 55-75 degrees. The fuel screw was turned out 2.5 and it wouldn't even fire. I turned it to 1.5 and now it backfires every few kicks and every once in a while it starts running for a second then shuts off and starts backfiring again. Could i have to rejet it? It has the stock jetting right now. Any help would be appreciated. This is really frustrating. By the way this is a 2002 yz426.