Anyone had any problems with backfiring issues on these it's a 2007 trx 450r. I've an MSR fuel screw,quickshot 2 lower bowl piece, UNI filter, full motorworks plus exhaust. No air box mods and no motor work. I've messed with the fuel screw as much as possible and I put a stage two jet kit, new needle and bigger main jet. It only backfires when I let off the gas at all speeds, it doesn't seem to effect anything it is fast as hell but it is more annoying than anything. Didn't know if anyone has heard of this problem, it did it from day one all the mods were to try and eliminate it.