I am learning that the newer yz450f carbs have had alot of upgrades to them ex: stronger AP spring and dont need all the mods since I am not having any problems with it now. My next question is needles. My JD Jet kit came with 2 needles. When I rejet the bike for my new FMF 4.1 exhaust should I use the red or blue needle? I live in ohio where altitude is around 700 to 800 above sea level or should I stick with the stock needle when rejetting the bike? Does my carb already have abetter needle in it? Thanks for any input!!!