I am 45 yrs old and have been riding all my life. I got away from 2 strokes for many reasons years ago, but miss the performance. I currently have a 2004 XR400 which I love the low end torque, smoothness and quietness of the 4 stroke and reliability and ltd maintenance. However i find myself looking for more power. What is a good, reliable modest upgrade to it, i.e. Pipe, Air Filter, jet etc. I am in MASS. so close to sea level, I am open to all ideas and willing to spend about $600-800 tops and i can do some of the work myself. Thanks.