Hi there, i recomend you go on a dyno for jetting. Just bying a set of needles from from f.instnace JD is not gonna get you spot on. Every bike is a littlebit different and so is the climate and (gas) your bike is exposed to. I have tried Yoshimura offroad alu on mine and guess what... the power and torque was greater with the standard pipes with the end/ sparkarrester removed. Airbox must be opened thoroughly, but don't do that before you have "richened" the engine by giving it more gas, it is set up very lean. chaning to a more open exhaust will lean some, opening the airbox makes a big difference. If your engine runs lean it will pop, stop and you can eventually damage the valves due to overheating. Fuel also cools....... A dyno run/ jetting should cost you more than 100 USD. We pulled out 8 hp around 6.000 rpm just by getting thing right. I doubt if a W.Brother and JD set will give you that unless you fine tune. don't guess... know for certain!