I have got to say I did not think this was going to happen. I thought I had my 500 tuned to make pretty good power, but my cousin just ran by me on a 07 yz250. He said his bike only has a pipe,wisco piston, and carb jetted. This is what my bike has gnarly pipe, k&n airfilter, and I leaned out the carb one point on the main jet. I just do not get it. The 500 seems to be running great, very smooth and powerful, but I guess not as powerful as I thought. I just do not know if my tire is spinning too much or what. I just put a new Kenda 771 on it. It seems where ever I go I leave a trench. One thing though, I think I am going to switch back to the stock filter. It seems to be better than the K&N.