I just bought a DG Stage-2 Xellerator Exhaust for my 400EX (2003) . The Exhaust is the only modifacation's i have done to the quad, for some reason when i put it on the Spark Plug's seem to be needing replaced every few days and when i take it out there is a good bit of carben build up on it. I belive to solve the problem i need a Jet Kit what kind and size would work best with the exhaust and the 400EX. But beside the evident probablem i love the exhaust and the power. Thanks to any suggestion's

 

thats funny how an aftermarket exhaust can make an engine run rich, it should be unning lean without a jet kit, try adjusting your silencer to make it flow more freely, it is adjustable isnt it?