400ex upgrades?

Stage 1 is probably best for a gncc bike. It will give you a little more low end grunt. I wouldn't run it much with just the header :/ that can make it really lean with increased flow and also the motor doesn't have any back pressure. Which might not hurt a thing, but i wouldn't chance it. If I was buying a new exhaust system for a 400ex it would be a HMF full system or a Pro-Circuit which is a slip on only for the 400ex I believe. HMF full systems are real nice looking and a solid build with increased flow. As for jets I can't really recommend any because each bike is different. You want the motor to run clean and crisp with no popping on deccel. At WOT your on strictly your main jet and if it blubbers and doesn't clean up you have to big of a main jet. At the same time if you bring it up to WOT and it cuts out and makes a lot of popping a sputtering on the decell (when you let off) then it is to lean. You have to try to find a happy medium. Checking the plug is also a very useful tool. If its white hot its too lean and if it is black and really sooty then it is too rich. Raising the needle up a notch will make your mid range get more fuel and lowering it will make it receive less fuel respectively. And last but not least, your pilot jet. This jet is only used idle-just off idle so if it idles good and doesn't idle up real high when it gets hot then you usually are okay. If it idles high and you can't slow the idle up with the adjustment then chances are it is lean on the pilot. I hope these tips help you decide which exhaust to buy and jet it correctly. I am sure there are other posts about jetting you can read up on to.