put on a techno circuit exhaust on my otherwise stock maxi 2.0 hp, 12mm bing with 64 jet. i can feel the improvement in torque. the top speed is around 29 mph (about 1 mph faster than stock exhaust). I tried a couple of bigger jets (66, 68) and they made it much slower (like 25 mph). I am going to try a cone type filter and see if that makes it a little quicker. Then maybe a 14mm carb if that shows no improvement. I would like to get it to 35mph with the circuit pipe if possible.