I have an 04 wr450,and have done all of the free mods- Since I do not ride in state parks, I took out the muffler baffle, and bike really runs well.- But I do have a small stumble down low. The info I read says the boysen pump will stop that. I have not changed the needle valve position, and I did not touch the mixture screw. My plan is to get the after market mixture screw, and the pump. Being farly new to this off road hobby, I figured all ofthe experience here could help- Do you folks think that these 2 mods will help? It is such a small hesitation, I really did not notice it- until I rode my friends 06 wr with all of the mods, including the GYT-R pipe and jet kit. So of course now mine is a slug I should have stayed off of it.